Electroplating apparatus for tailored uniformity profile

ABSTRACT

Methods of electroplating metal on a substrate while controlling azimuthal uniformity, include, in one aspect, providing the substrate to the electroplating apparatus configured for rotating the substrate during electroplating, and electroplating the metal on the substrate while rotating the substrate relative to a shield such that a selected portion of the substrate at a selected azimuthal position dwells in a shielded area for a different amount of time than a second portion of the substrate having the same average arc length and the same average radial position and residing at a different angular (azimuthal) position. For example, a semiconductor wafer substrate can be rotated during electroplating slower or faster, when the selected portion of the substrate passes through the shielded area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation claiming priority to U.S. patentapplication Ser. No. 14/483,942, titled “Electroplating Apparatus forTailored Uniformity Profile” naming Mayer et al. as inventors, filedSep. 11, 2014, which is a continuation claiming priority to U.S. patentapplication Ser. No. 13/438,443, titled “Electroplating Apparatus forTailored Uniformity Profile” naming Mayer et al. as inventors, filedApr. 3, 2012 (issued as U.S. Pat. No. 8,858,774 on Oct. 14, 2014), whichclaims benefit under 35 U.S.C. §119(e) to U.S. Provisional PatentApplication No. 61/471,624, titled “Electroplating Apparatus forTailored Uniformity Profile”, naming Mayer et al. as inventors, filedApr. 4, 2011 and to U.S. Provisional Patent Application No. 61/598,054,titled “Electroplating Apparatus for Uniform Electrolyte FlowDistribution” naming Buckalew et al. as inventors, filed Feb. 13, 2012,which are herein incorporated by reference. U.S. patent application Ser.No. 13/438,443 is also a continuation-in-part claiming priority to U.S.patent application Ser. No. 12/291,356, titled “Method and Apparatus forElectroplating” naming Reid et al. as inventors, filed Nov. 7, 2008, nowU.S. Pat. No. 8,308,931, issued Nov. 13, 2012, which is hereinincorporated by reference.

FIELD OF THE INVENTION

The present disclosure relates generally to method and apparatus forelectroplating a metal layer on a semiconductor wafer. Moreparticularly, the method and apparatus described herein are useful forcontrolling plating uniformity.

BACKGROUND

The transition from aluminum to copper in integrated circuit (IC)fabrication required a change in process “architecture” (to damasceneand dual-damascene) as well as a whole new set of process technologies.One process step used in producing copper damascene circuits is theformation of a “seed-” or “strike-” layer, which is then used as a baselayer onto which copper is electroplated (“electrofill”). The seed layercarries the electrical plating current from the edge region of the wafer(where electrical contact is made) to all trenches and via structureslocated across the wafer surface. The seed film is typically a thinconductive copper layer. It is separated from the insulating silicondioxide or other dielectric by a barrier layer. The seed layerdeposition process should yield a layer which has good overall adhesion,excellent step coverage (more particularly, conformal/continuous amountsof metal deposited onto the side-walls of an embedded structure), andminimal closure or “necking” of the top of the embedded feature.

Market trends of increasingly smaller features and alternative seedingprocesses drive the need for a capability to plate with a high degree ofuniformity on increasingly thin seeded wafers. In the future, it isanticipated that the seed film may simply be composed of a plateablebarrier film, such as ruthenium, or a bilayer of a very thin barrier andcopper (deposited, for example, by an atomic layer deposition (ALD) orsimilar process). Such films present the engineer with an extremeterminal effect situation. For example, when driving a 3 amp totalcurrent uniformly into a 30 ohm per square ruthenium seed layer (alikely value for a 30-50 Å film) the resultant center to edge (radial)voltage drop in the metal will be over 2 volts. To effectively plate alarge surface area, the plating tooling makes electrical contact to theconductive seed only in the edge region of the wafer substrate. There isno direct contact made to the central region of the substrate. Hence,for highly resistive seed layers, the potential at the edge of the layeris significantly greater than at the central region of the layer.Without appropriate means of resistance and voltage compensation, thislarge edge-to-center voltage drop could lead to an extremely non-uniformplating rate and non-uniform plating thickness distribution, primarilycharacterized by thicker plating at the wafer edge. This platingnon-uniformity is radial non-uniformity, that is, uniformity variationalong a radius of the circular wafer.

Another type of non-uniformity, which needs to be mitigated, isazimuthal non-uniformity. For clarity, we define azimuthalnon-uniformity, using polar coordinates, as thickness variationsexhibited at different angular positions on the workpiece at a fixedradial position from the wafer center, that is, a non-uniformity along agiven circle or portion of a circle within the perimeter of the wafer.This type of non-uniformity can be present in electroplatingapplications, independently of radial non-uniformity, and in someapplications may be the predominant type of non-uniformity that needs tobe controlled. It often arrises in through resist plating, where a majorportion of the wafer is masked with a photoresist coating or similarplating-preventing layer, and the masked pattern of features or featuredensities are not azmuthally uniform near the wafer edge. For example,in some cases there may be a technically required chord-region ofmissing pattern features near the notch of the wafer to allow for wafernumbering or handling. The radially and azimuthally variable platingrates inside missing region may cause chip die to be non-functional,therefore methods and apparatus for avoiding this situation are needed.

Electrochemical deposition is now poised to fill a commercial need forsophisticated packaging and multichip interconnection technologies knowngenerally as wafer level packaging (WLP) and through silicon via (TSV)electrical connection technology. These technologies present their ownvery significant challenges.

These technologies require electroplating on a significantly larger sizescale than damascene applications. Depending on the type and applicationof the packaging features (e.g. through chip connecting TSV,interconnection redistribution wiring, or chip to board or chip bonding,such as flip-chip pillars), plated features are usually, in currenttechnology, greater than about 2 micrometers in diameter and typicallyare 5-100 micrometers in diameter (for example, pillars may be about 50micrometers). For some on-chip structures such as power busses, thefeature to be plated may be larger than 100 micrometers. The aspectratios of the WLP features are typically about 2:1 (height to width) orlower, more typically 1:1 or lower, while TSV structures can have veryhigh aspect ratios (e.g., in the neighborhood of about 10:1 or 20:1).

Given the relatively large amount of material to be deposited, not onlyfeature size, but also plating speed differentiates WLP and TSVapplications from damascene applications. For many WLP applications,plating must fill features at a rate of at least about 2micrometers/minute, and typically at least about 4 micrometers/minute,and for some applications at least about 7 micrometers/minute. Theactual rates will vary depending on the particular metal beingdeposited. But at these higher plating rate regimes, efficient masstransfer of metal ions in the electrolyte to the plating surface is veryimportant. Higher plating rates present challenges with respect touniformity of the electrodeposited layer.

SUMMARY OF THE INVENTION

Described are method and apparatus for controlling plating uniformity,particularly, azimuthal non-uniformity, radial non-uniformity, or both.Apparatus and methods described herein can be used for electroplating ona variety of substrates, including semiconductor wafer substrates havingTSV or WLP recessed features.

In some embodiments, a method for electroplating an asymmetrical platingworkpiece (including a geometrically symmetrical workpiece substratewhose exposed area to be plated is asymmetrical, such as a wafer with anazimuthally non-uniformly patterning), is provided. The asymmetry refersnot only to purely geometric asymmetry of the substrate (such aspresence of a notch, or a flat region cut along a chord), but also toasymmetry within the features on the substrate, which may result inunwanted ionic current crowding during plating, and lead to increasedplating at certain azimuthal regions of the wafer. For example, in someembodiments electroplating is performed on a substrate having a missingdie. Electroplating on such substrate leads to current crowding in theareas that are adjacent to the azimuthal variable patterningdiscontinuities at the periphery, such as a region with missing featuresand missing die, and, consequently, to plating non-uniformity in thisregion.

Provided methods and apparatus, in some embodiments, employ azimuthallyasymmetric shields—shields that provide shielding from the plating(ionic) current to a greater degree at some azimuthal (angular)positions than at other azimuthal (angular) positions, at least at oneof radial positions.

Provided methods and apparatus, in some embodiments, employ azimuthallyasymmetric auxiliary electrodes—electrodes configured to divert platingcurrent (auxiliary cathodes or thieves), to donate plating current(auxiliary anodes), or to both donate and divert current at differenttime points (referred to as anode/cathodes), where the electrodes areshaped or confined such as to predominantly modify current to a greaterdegree at some azimuthal (angular) positions in preference to otherpositions.

An example of an azimuthally asymmetric electrode is a C-shapedelectrode (a cathode, anode, or an anode/cathode). The C-shapedelectrode, is located, in some embodiments, relatively close to thewafer substrate (e.g., within a distance of not greater than 0.2 of theradius of the wafer), and is electrically connected to a power supplyand a controller, which, in some embodiments, provide for it beingenergized in correlation with rotation of the wafer. In some embodimentsthe body of the C-shaped electrode, preferably, has an arc length ofless than about 120 degrees, such as less than about 90 degrees.

In one aspect, provided methods and apparatus employ azimuthallyasymmetric shields and/or azimuthally asymmetric auxiliary electrodesand/or multi-segmented auxiliary electrodes, where rotation of the waferis adjusted such that different angular (azimuthal) positions of thewafer have different dwell times in the shielded area or in the areaproximate the auxiliary electrode or its segment.

Thus, for example, a missing die area may spend more time, on average,in a relatively more shielded area than an equivalent portion of thewafer at a different angular (azimuthal) position but having the sameaverage arc length and same average radial position.

In another aspect, provided methods and apparatus employ azimuthallyasymmetric auxiliary electrodes and/or multi-segmented auxiliaryelectrodes, where the electrodes are energized in correlation with therotation of the wafer such that different angular (azimuthal) positionsof the wafer are exposed to different amounts of plating current beingdonated and/or diverted by an auxiliary electrode (or electrodesegment).

For example, a C-shaped auxiliary electrode may be energized incorrelation with the rotating wafer, e.g., such as when the missing dieregion of the wafer passes through proximity of the C-shaped electrode,the electrode may be energized at a first level (e.g., to divert currentat a first level), while it is energized at a different level, or notenergized, or energized to have an opposite polarity, when otherazimuthal (angular) positions of the wafer pass through its proximityduring the course of wafer rotation. The terms angular and azimuthalpositions are synonymous and can be used interchangeably.

It should be understood that the all secondary or auxiliary electrodefunctionality described herein can be operated as either anodes,cathodes, or both. The anode may be an inert anode or dimensionallystable anode, for example generating oxygen gas, or it can be a metallicanode, creating metal ions. The cathode may have metal platingthereupon, or may undergo another cathodic reaction, such as hydrogenevolution (e.g. if plateable metal ions are excluded from theelectrode's surface). The electrode may, in some embodiments, combinetwo or more of the above processes, changing in time during a waferplating cycle (an anode/cathode). Therefore, while some embodimentsdescribed herein, are exemplified, by thief cathodes, it is understoodthat all of these embodiments can be used not only with thief cathodes,but with other types of auxiliary electrodes, including anodes(positively biased electrodes configured for donating plating current)and anode/cathodes (electrodes, which can be biased both negatively andpositively, at different time points as desired). The auxiliaryelectrodes may be energized either continuously or for some portion ofthe rotation of the wafer.

Further, while it may not be mentioned with each of the methodsdescribed, preferably each method includes an operation prior toelectroplating in which the desired azimuthal position of the substrateis registered (e.g., by an optical device), such that this position isknown, and such that the apparatus could be programmed, such as toprovide appropriate plating current correction for this specificposition (or for a different position residing at a certain angle fromthe known position) during the course of electroplating. Theregistration of the selected angular position (e.g., a notch) can beperformed in the electroplating apparatus, or in a different apparatus,as long as the recorded position remains known, up to the point ofelectroplating.

In one aspect, a method of electroplating a metal on a cathodicallybiased substrate while controlling azimuthal uniformity, includesproviding the substrate into an electroplating apparatus configured forrotating the substrate during electroplating, wherein the apparatuscomprises an anode and a stationary auxiliary azimuthally asymmetricelectrode; and electroplating the metal on the substrate while rotatingthe substrate, and while providing power to the auxiliary azimuthallyasymmetric electrode in correlation with the rotation of the substrate,such that the auxiliary azimuthally asymmetric electrode diverts and/ordonates plating current to a first portion of the substrate at aselected azimuthal position of the substrate differently than to asecond portion of the substrate having the same average arc length andthe same average radial position and residing at a different azimuthalangular position.

It is understood that providing desired power to the auxiliary electrodecan be achieved by controlling current, voltage or combination thereoffrom a power supply electrically connected to the auxiliary electrode.The auxiliary electrode can be energized such that a different currentis applied to it when the selected azimuthal position passes in itsproximity, while the auxiliary electrode may be energized by a differentlevel of current, not energized at all, or energized at a differentpolarity, when other angular positions of the wafer pass through itsproximity. Typically, during one full rotation of the wafer theauxiliary electrode passes through at least two distinct states (e.g.,energized by different levels of current, energized at differentpolarities, or energized/non-energized states).

In some embodiments the azimuthally asymmetric electrode is C-shaped. Insome embodiments the electrode may reside in an azimuthal current flowconfinement structure. If the confinement structure provides an exposureof plating current (e.g., through a slot or a series of openings) thatapproximates a C-shape, the auxiliary electrode itself may have avariety of shapes, because the modification of plating current by theauxiliary electrode will be governed by the exposure created by theconfinement structure. In some embodiments, the auxiliary azimuthallyasymmetric electrode is housed in a separate chamber and the exposure ofplating current from the auxiliary electrode is through at least onechannel that delivers current into a region of the cell near theperiphery of the substrate over an arc angle of less than about 120degrees.

In some embodiments, the auxiliary azimuthally asymmetric electrode iscathodically biased and is configured to divert different amounts ofplating current from different azimuthal positions of the substrateduring electroplating. For example, during one full rotation of thewafer, the electrode may accept a first level of cathodic current (whenthe selected angular position of the rotating wafer passes in itsproximity) and then a different (lower or higher) level of current (whena different angular position passes through its proximity). In anotherexample, during one full rotation of the wafer, the electrode may accepta first level of cathodic current (when the selected angular position ofthe rotating wafer passes in its proximity) and then may remainnon-energized (when a different angular position passes through itsproximity).

In other embodiments, the auxiliary azimuthally asymmetric electrode isanodically biased and is configured to donate different amounts ofplating current to different azimuthal positions of the substrate duringelectroplating. For example, during one full rotation of the wafer, theelectrode may accept a first level of anodic current (when the selectedangular position of the rotating wafer passes in its proximity) and thena different (lower or higher) level of current (when a different angularposition passes through its proximity). In another example, during onefull rotation of the wafer, the electrode may accept a first level ofanodic current (when the selected angular position of the rotating waferpasses in its proximity) and then may remain non-energized (when adifferent angular position passes through its proximity).

In other embodiments, the auxiliary azimuthally asymmetric electrode isboth anodically and cathodically biased during electroplating, and isconfigured to divert plating current from a first azimuthal position onthe substrate and to donate plating current to a second azimuthalposition on the substrate. For example, during one full rotation of thewafer, the electrode may accept a level of anodic current (when theselected angular position of the rotating wafer passes in its proximity)and then a level of cathodic current (when a different angular positionof the rotating wafer passes through its proximity). Such anode/cathodeis typically electrically connected to a bipolar power supply, which isconfigured to change polarity of the auxiliary electrode, as necessary.

In some embodiments, the electroplating apparatus includes a shield,shielding the periphery of the substrate at all azimuthal positions, andthe auxiliary azimuthally asymmetric electrode is anodically biased atleast during a portion of a time of a full rotation of the substrate,and is configured to donate current to the selected azimuthal positionon the substrate. By using the azimuthally symmetrical shield, theentire periphery of the wafer may be lacking in plating current, whichcan be corrected by donating plating current at different levels todifferent angular positions, by an auxiliary anode.

In another aspect, a method of electroplating a metal on a cathodicallybiased substrate includes providing the substrate into an electroplatingapparatus configured for rotating the substrate during electroplating,wherein the apparatus comprises an auxiliary azimuthally asymmetric ormulti-segmented anode in the proximity of the substrate; andelectroplating the metal on the substrate while rotating the substrate,and while providing power to the auxiliary azimuthally asymmetric anodeat a substantially constant level to donate current to the substrate.

In another aspect an electroplating apparatus for electroplating a metalon a substrate is provided, where the apparatus includes a platingchamber configured to contain an electrolyte, an anode, and anazimuthally asymmetric auxiliary electrode; a substrate holderconfigured to hold the substrate; and a controller comprising programinstructions for electroplating the metal on the substrate whilerotating the substrate, and while providing power to the auxiliaryazimuthally asymmetric electrode in correlation with the rotation of thesubstrate, such that the auxiliary azimuthally asymmetric electrodediverts and/or donates plating current to a first portion of thesubstrate at a selected azimuthal position of the substrate differentlythan to a second portion of the substrate having the same average arclength and the same average radial position and residing at a differentangular azimuthal position. In some embodiments this apparatus isintegrated into a system configured for photolithographic processingwhich further includes a stepper.

In another aspect a non-transitory computer machine-readable mediumcomprising program instructions for control of an electroplatingapparatus is provided, wherein the program instructions include code forelectroplating the metal on the substrate while rotating the substrate,and while providing power to the auxiliary azimuthally asymmetricelectrode in correlation with the rotation of the substrate, such thatthe auxiliary azimuthally asymmetric electrode diverts and/or donatesplating current to a first portion of the substrate at a selectedazimuthal position of the substrate differently than to a second portionof the substrate having the same average arc length and the same averageradial position and residing at a different angular azimuthal position.

In some embodiments the methods provided herein are integrated into thegeneral processing schemes that include photolithographic processing,and further include the steps of applying photoresist to the substrate;exposing the photoresist to light; patterning the resist andtransferring the pattern to the workpiece; and selectively removing thephotoresist from the work piece. In some embodiments, the photoresist isapplied and patterned prior to electroplating and is removed afterelectroplating.

In another aspect, an electroplating apparatus for electroplating ametal on a substrate, is provided, wherein the apparatus includes: aplating chamber configured to contain an electrolyte; a substrate holderconfigured to hold and rotate the substrate during electroplating; ananode; and an azimuthally asymmetric auxiliary electrode configured tobe biased both anodically and cathodically during electroplating.

In another aspect an electroplating apparatus for electroplating a metalon a substrate is provided, wherein the apparatus includes: a platingchamber configured to contain an electrolyte; a substrate holderconfigured to hold and rotate the substrate during electroplating; ananode; a shield configured to shield current at the periphery of thesubstrate; and an azimuthally asymmetric auxiliary anode configured todonate current to the shielded periphery of the substrate at a selectedazimuthal position on the substrate.

In another aspect an electroplating apparatus for electroplating a metalon a substrate is provided, where the apparatus includes: a platingchamber configured to contain an electrolyte; a substrate holderconfigured to hold and rotate the substrate during electroplating; ananode; and a multi-segmented auxiliary electrode configured to be biasedboth anodically and cathodically during electroplating, or amulti-segmented auxiliary anode.

In another aspect, a method of electroplating a metal on a cathodicallybiased substrate while controlling azimuthal uniformity includes: (a)providing the substrate into an electroplating apparatus configured forrotating the substrate during electroplating, wherein the apparatuscomprises a first anode and a multi-segmented auxiliary anode or amulti-segmented auxiliary electrode configured to serve both as anauxiliary anode and an auxiliary cathode; and (b) electroplating themetal on the substrate while rotating the substrate, and while providingpower to the segments of the multi-segmented auxiliary anode or themulti-segmented auxiliary electrode in correlation with the rotation ofthe substrate, such that said anode donates plating current to a firstportion of the substrate at a selected azimuthal position of thesubstrate to a different level than to a second portion of the substratehaving the same average arc length and the same average radial positionand residing at a different angular azimuthal position, or such thatsaid auxiliary electrode donates current to the first portion anddiverts the current from the second portion.

In another aspect a method of electroplating a metal on a substratewhile controlling azimuthal uniformity includes: (a) providing thesubstrate into an electroplating apparatus configured for rotating thesubstrate during electroplating; and (b) electroplating the metal on thesubstrate while rotating the substrate relative to a shield such that aselected portion of the substrate at a selected azimuthal positiondwells in a shielded area for a different amount of time than a secondportion of the substrate having the same average arc length and the sameaverage radial position and residing at a different angular azimuthalposition.

For example, the substrate may be rotated at a first speed when theselected portion of the substrate is less shielded, and at a secondspeed when the selected portion of the substrate is more shielded,wherein one full rotation of the substrate comprises a first period ofrotation at the first speed and a second period of rotation at thesecond speed. In some embodiments, the second speed is lower than thefirst speed, that is, the substrate slows down when the selected angularposition of the wafer (usually the one affected by current crowding)passes through the more shielded area. In a more specific example, thefirst speed is at least about 20 rpm, the second speed is less thanabout 10 rpm, and the substrate makes at least about 5 variable-speedfull rotations during the course of electroplating.

In some embodiments, different dwell times in the shielded area areachieved by rotating the substrate bidirectionally at a constant speed.The bidirectional rotation is configured such that the selected angularposition of the wafer spends more (or less) time in the shielded area incomparison with other angular positions.

Preferably, the distance between the shield and the platable surface ofthe substrate is no more than about 0.1 of the radius of the substrate.In some embodiments, the distance between the shield and the platablesurface of the substrate is no more than about 4 mm.

In some embodiments the electroplating apparatus further comprises anionically resistive ionically permeable element having a flat surfacethat is substantially parallel to and separated from the plating face ofthe substrate by a distance of about 10 millimeters or less duringelectroplating, wherein the element has a plurality of non-communicatingholes. In some embodiments, the shield is an azimuthally asymmetricshield eclipsing some of the holes of the ionically resistive ionicallypermeable element or the shield itself is the ionically resistiveionically permeable element having an azimuthally asymmetricdistribution of hoes.

In one aspect an electroplating apparatus for electroplating a metal ona substrate is provided, where the apparatus includes: a plating chamberconfigured to contain an electrolyte and a shield; a substrate holderconfigured to hold the substrate; and a controller comprising programinstructions for electroplating the metal on the substrate whilerotating the substrate relative to the shield such that a selectedportion of the substrate at a selected azimuthal position dwells in ashielded area for a different amount of time than a second portion ofthe substrate having the same average arc length and the same averageradial position and residing at a different angular azimuthal position.In another aspect, a system comprising such apparatus and a stepper isprovided.

In another aspect, a non-transitory computer machine-readable mediumcomprising program instructions for control of an electroplatingapparatus, is provided, where the program instructions include code forelectroplating metal on a substrate while rotating the substraterelative to a shield such that a selected portion of the substrate at aselected azimuthal position dwells in a shielded area for a differentamount of time than a second portion of the substrate having the sameaverage arc length and the same average radial position and residing ata different angular azimuthal position.

In another aspect a method of electroplating a metal on a substratewhile controlling azimuthal uniformity is provided, where the methodincludes: providing the substrate into an electroplating apparatusconfigured for rotating the substrate during electroplating, wherein theelectroplating apparatus comprises a multi-segmented auxiliary electrodeconfigured to divert and/or donate current during electroplating; and(b) electroplating the metal on the substrate while rotating thesubstrate relative to the stationary multi-segmented auxiliary electrodesuch that a selected portion of the substrate at a selected azimuthalposition dwells in an area proximate to a segment of the auxiliaryelectrode for a different amount of time than a second portion of thesubstrate having the same average arc length and the same radialposition and residing at a different angular azimuthal position, andwherein at least one segment of the auxiliary electrode diverts and/ordonates plating current differently than another segment. For example,one of the segments may be accept a current at a different level thanother segments (anodic or cathodic), or one of the segments may have theopposite polarity from the other segments.

In another aspect, a method of electroplating a metal on a substratewhile controlling azimuthal uniformity includes: providing the substrateinto an electroplating apparatus configured for rotating the substrateduring electroplating, wherein the electroplating apparatus comprises anazimuthally asymmetric auxiliary electrode configured to divert and/ordonate current during electroplating; and electroplating the metal onthe substrate while rotating the substrate relative to the azimuthallyasymmetric auxiliary electrode such that a selected portion of thesubstrate at a selected azimuthal position dwells in an area proximateto the azimuthally asymmetric auxiliary electrode for a different amountof time than a second portion of the substrate having the same averagearc length and the same average radial position and residing at adifferent angular azimuthal position.

In another embodiment a method of electroplating a metal on a substratewhile controlling azimuthal uniformity includes: (a) providing thesubstrate into an electroplating apparatus configured for rotating thesubstrate during electroplating, wherein the electroplating apparatuscomprises a rotatable multi-segmented thief cathode configured to divertcurrent during electroplating; and (b) electroplating the metal on thesubstrate while rotating the substrate and the thief cathode at the samespeed such that a selected portion of the substrate at a selectedazimuthal position dwells in an area proximate to a segment of the thiefcathode for a different amount of time than a second portion of thesubstrate having the same average arc length and the same average radialposition and residing at a different angular azimuthal position.

In another embodiment, a method of electroplating a metal on a substratewhile controlling azimuthal uniformity includes (a) providing thesubstrate into an electroplating apparatus configured for rotating thesubstrate during electroplating, wherein the electroplating apparatuscomprises a rotatable azimuthally asymmetric thief cathode configured todivert current during electroplating; and (b) electroplating the metalon the substrate while rotating the substrate and the thief cathode atthe same speed such that a selected portion of the substrate at aselected azimuthal position dwells in an area proximate to the thiefcathode for a different amount of time than a second portion of thesubstrate having the same average arc length and the same average radialposition and residing at a different angular azimuthal position.

In another embodiment, a method of electroplating a metal on a substratewhile controlling azimuthal uniformity includes providing the substrateinto an electroplating apparatus configured for rotating the substrateduring electroplating, wherein the electroplating apparatus comprises arotatable multi-segmented auxiliary anode configured to divert currentduring electroplating or a rotatable multi-segmented auxiliary electrodeconfigured to function both as an anode and a cathode; andelectroplating the metal on the substrate while rotating the substrateand the multi-segmented auxiliary anode or the multi-segmented auxiliaryelectrode at the same speed such that a selected portion of thesubstrate at a selected azimuthal position dwells in an area proximateto a segment of the anode or the electrode for a different amount oftime than a second portion of the substrate having the same average arclength and the same average radial position and residing at a differentangular azimuthal positions.

In another embodiment a method of electroplating a metal on a substratewhile controlling azimuthal uniformity includes: (a) providing thesubstrate into an electroplating apparatus configured for rotating thesubstrate during electroplating, wherein the electroplating apparatuscomprises a rotatable azimuthally asymmetric anode configured to divertcurrent during electroplating or a rotatable azimuthally asymmetricanode/cathode configured to both divert and donate current duringelectroplating; and (b) electroplating the metal on the substrate whilerotating the substrate and the anode or anode/cathode at the same speedsuch that a selected portion of the substrate at a selected azimuthalposition dwells in an area proximate to the anode or the anode/cathodefor a different amount of time than a second portion of the substratehaving the same average arc length and the same average radial positionand residing at a different angular azimuthal position.

In some embodiments, all methods presented herein may further includerotating a shield having a generally annular body with a removedsegment, which resides in close proximity of the wafer, during thecourse of electroplating. This can optimize the flow of electrolyte inthe proximity of the wafer as the electrolyte will tend to movelaterally at the wafer surface in the direction of the opening of thatshield. In some embodiments this flow diverter is rotated at a speedthat is different from the wafer rotation speed, thereby maximizingrandomization of the flow patterns.

For all methods disclosed herein, the selected portion of the substratemay include an area adjacent to a wafer notch, a wafer flat or a set ofazimuthally missing features, which is registered (e.g., by an opticalaligner) prior to electroplating. Electroplating, in some embodimentsincludes filling recessed features during TSV or WLP processing.

These and other features and advantages of the present invention will bedescribed in more detail below with reference to the associateddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B show schematic top views of an asymmetrical wafer rotatingin the presence of a multi-segmented thief cathode, energized incorrelation with the wafer rotation.

FIGS. 2A-2B show top views of an asymmetrical plate having differentdistribution of non-communicating holes functioning as an azimuthallyasymmetric shield.

FIG. 3A shows a view of a plate with non-communicating holes and ashield.

FIG. 3B shows a cross-sectional view of an assembly illustrated in FIG.3A, in relation to the wafer and wafer holder.

FIG. 4A illustrates top view of a variety of azimuthally asymmetricshields residing over a plate having non-communicating holes.

FIG. 4B illustrates shields, which are further configured to correctradial non-uniformity.

FIGS. 5A-5F illustrate shields in accordance with embodiments presentedherein.

FIG. 6 shows a top view of a bidirectionally rotating wafer in a systemcontaining azimuthally asymmetric shielding.

FIG. 7 is a process flow diagram for a process in accordance with one ofthe embodiments.

FIG. 8 is a process flow diagram for a process in accordance with one ofthe embodiments.

FIG. 9 is a schematic cross-sectional view of an electroplatingapparatus in accordance with an embodiment provided herein.

FIGS. 10A-10C illustrate rotation of an asymmetrical wafer in anapparatus having a C-shaped auxiliary electrode, energized incorrelation with the wafer rotation.

FIG. 11 shows a schematic top view of a plating cell with an azimuthallyasymmetric auxiliary electrode in a confinement structure.

FIG. 12 shows an isometric view of a structure housing the C-shapedauxiliary electrode in accordance with an embodiment provided herein.

DETAILED DESCRIPTION

Methods and apparatus for electroplating a metal on a substrate whilecontrolling uniformity of the electroplated layer, such as azimuthaluniformity, radial uniformity, or both, are provided.

Embodiments are described generally where the substrate is asemiconductor wafer; however the invention is not so limited. Providedapparatus and methods are useful for electroplating metals in TSV andWLP applications, but can also be used in a variety of otherelectroplating processes, including deposition of copper in damascenefeatures. Examples of metals that can be electroplated using providedmethods include, without limitation, copper, tin, a tin-leadcomposition, a tin-silver composition, nickel, cobalt, nickel and/orcobalt alloys with each other and with tungsten, a tin-coppercomposition, a tin-silver-copper composition, gold, palladium, andvarious alloys which include these metals and compositions.

In a typical electroplating process, the semiconductor wafer substrate,which may have one or more recessed features on its surface is placedinto the wafer holder, and its platable surface is immersed into anelectrolyte contained in the electroplating bath. The wafer substrate isbiased negatively, such that it serves as a cathode duringelectroplating. The ions of the platable metal (such as ions of metalslisted above) which are contained in the electrolyte are being reducedat the surface of the negatively biased substrate during electroplating,thereby forming a layer of plated metal. The wafer, which is typicallyrotated during electroplating, experiences an electric field (ioniccurrent field of the electrolyte) that may be non-uniform for a varietyof reasons, including azimuthal asymmetry existing in the wafersubstrate. This may lead to non-uniform deposition of metal.

The electroplating apparatus provided herein typically includes asubstrate holder configured for holding and rotating the substrateduring electroplating; a plating bath configured for holding anelectrolyte and an anode; and a power supply having a negative terminalelectrically connected to the wafer substrate, and a positive terminalelectrically connected to the anode. The apparatus further includes oneor more elements, such as shields, and auxiliary electrodes (cathodes,anodes or anode/cathodes), that are configured for tailoring uniformityprofile during plating. The apparatus, in some embodiments, furtherincludes a controller having program instructions for performing methodsdisclosed herein, such as for varying rotational speed and/or rotationaldirection of the substrate in a manner that allows controlling platinguniformity. The controller, in some embodiments, further includesprogram instructions for energizing auxiliary electrodes in correlationwith the wafer rotation.

The present disclosure relates to method and apparatus for controllingplating uniformity particularly, not only radial non-uniformity but alsoazimuthal non-uniformity. Azimuthal non-uniformity can arise in a numberof ways. In one example, semiconductor wafers are sometimes cut along achord (e.g. JEDA wafers) and have a notch, e.g. for registrationpurposes during process manipulations. These chords or notchesconstitute azimuthal non-uniformities in the wafer. As the wafer isrotated and exposed to a plating field, the edges of the wafer along thechord or notch are exposed to different field strength than othercorresponding areas of the wafer along the same annulus (i.e., sameradial position). During plating, there will be azimuthal non-uniformityfrom the edge of the chord or notch going inward toward the center areasof the wafer. As another example, a seed layer is typically deposited ona wafer that has been patterned with device features, or device featuresare patterned in a layer of photoresist overlying the seed layer on awafer that is substantially round (with the exception of a notch forangular registry). These device features are typically repeated as aseries of, for example, rectangular dies. Since the wafer itself isround, inevitably there are areas at the edge of the wafer where thereis insufficient room for a complete die with all the die device featuresor patterns (or where the topography is significantly different thanthat of the features as a whole). Because of this, there are inevitablyboundaries between the areas where there are no features (for exampleunexposed unpatterned resist) and the areas with features. Thereforealong a given annulus within the perimeter of the wafer, typically butnot necessarily toward the perimeter of the wafer, there are featurepattern variations, such as regions containing featured and othernon-featured surfaces. Because there are boundaries between featured andnon-featured (or topographically different) areas, there are necessarilyazimuthal plating variations due to the fact that the line of currentflow and the electric field is tailored to plate, for example, on aparticular topography a certain way and/or because, at these boundaries,there is a different topography and an excess exposure to the platingcell's field and lines of current, so plating current crowded or builtup at these transition locations. One way to overcome the topographychange would be to print partial (non-functional) features and dies tofill the areas where dies would not normally fit, extending the patternto the wafer edge, for example, all the way around the periphery of thewafer. However, since dies are commonly lithographed individually on thewafer, there is an associated prohibitive cost to forming these “dummy”features. These substrates will be referred to as azimuthally asymmetricsubstrates. Notably, such substrates may be geometrically asymmetric(e.g., have a notch or a cut-out portion and the substrate itself is notsubstantially round), or the asymmetry may be lie in the distribution ofthe features defined on the substrate (e.g., a missing set of featuresor die), or both. In an azimuthally asymmetric substrate, there isazimuthal variation of substrate geometry or substrate topography atleast at one radial position.

Azimuthal plating non-uniformity on substrates, particularly onazimuthally asymmetric substrates is addressed, in some embodiments, byusing azimuthally asymmetric shields and azimuthally asymmetricauxiliary electrodes and/or by using rotational techniques that alignselected azimuthal positions of the substrates with shielded areas orareas in the proximity of thief cathodes.

Azimuthally asymmetric shields are shields that shield the substratefrom plating current at some azimuthal positions, and not to the sameextent or not at all in other azimuthal positions, along at least oneradial position. These include wedge-shaped shields, batwing-shapedshields, etc. A purely annular shield (without protrusions to the centerof the annulus) is not azimuthally asymmetric with respect to a roundworkpiece such as a wafer. Shields are typically made of an ionicallyresistive material relative to the main plating solution media, and areplaced in the proximity of the wafer substrate to prevent unwantedexcessive current crowding at selected positions of the substrate. Insome cases the ionic resistance of the shield is not absolute, but isonly significantly greater than the plating media itself. In other casesthe shield has not only an azimuthally variable shape, but also has anazimuthally and/or radially variable ionic resistance, for example,created by having a variable pattern of holes in a resistive plate suchas a piece of plastic or ceramic. Generally the shields are electricallynon-conductive (they do not conduct electrical current by transport ofelectrons), and are therefore made of dielectric material such asplastics, glasses, and ceramics, and not made of metals. The shields aremost effective at tailoring azimuthal plating uniformity if the distancebetween the platable surface of the wafer and the closest surface of theshield is no more than about 0.1 times the radius of the substrate, suchas no more than about 0.2 of the radius of the substrate. As a specificexample, the azimuthal edge correcting shield according to thisinvention for a 300 mm diameter wafer would be closer than about 30 mm,more typically spaced less than 15 mm from the wafer substrate, forexample, about 7 mm from the wafer surface. In many embodiments, theshields are disposed in the plating bath, immersed in the electrolyte,very close to the substrate, such as within 4 mm of the platable surfaceof the substrate.

Azimuthally asymmetric thief cathodes are azimuthally asymmetricnegatively biased members (e.g., strips of metal), which are disposed inionic communication with the plating electrolyte (e.g., either directlyin the plating bath, or in an adjacent chamber in ionic communicationwith the wafer and wafer edge), where the thieves are configured fordiverting a portion of ionic plating current emanating from the mainanode placed generally below and aligned with the wafer away from thesubstrate to the thief cathode. Alternatively, the electrode may operateas an auxiliary anode, configured and operating for deliveringadditional ionic plating current, in excess of what would be suppliedfrom the main anode. In some embodiments the electrode can cycle itsoperation between both of these two modes, acting as an auxiliary anode,and later as an auxiliary cathode, both synchronized with the rotationof the wafer, such that the electrode is energized at a first leveland/or polarity when selected angular position of the rotating substratepasses through its proximity, and is energized at a different leveland/or with different polarity when a different angular position of therotating wafer passes through its proximity. Thus, during one fullrotation of the wafer the azimuthally asymmetric electrode has at leasttwo states (energized by applying two levels of current,energized/non-energized, or energized at different polarities).Anodes/cathodes can be energized by a bipolar power supply which allowsfor switching from cathode to anode mode without change in hardware.Auxiliary electrodes are typically biased and controlled separately fromthe substrate, e.g., using a separate power supply or resistivecontrolling circuitry, or a separate channel on the same power supplythat provides current to the substrate. Azimuthally asymmetricelectrodes such as thief cathodes, auxiliary anodes, and anode/cathodesmodify plating current at some azimuthal positions of the wafer to adifferent extent than at other azimuthal positions around at least oneradial position. An example of an azimuthally asymmetric thief, anode,or an anode/cathode is a C-shaped auxiliary electrode that surrounds thewafer periphery out beyond the radius of the wafer over only a portionof the wafer circumference (e.g., an annular thief having a segmentremoved). In some embodiments, the body of the C-shaped electrode has anarc length of less than about 120 degrees such as less than about 90degrees. An annular electrode, in contrast, is azimuthally symmetric andsurrounds the wafer entirely over the entire portion of thecircumference. In some embodiments the azimuthally asymmetric electrodesreside in close proximity to the wafer, e.g., preferably within adistance not greater than 0.2 times the radius of the wafer. In someembodiments, the azimuthally asymmetric electrodes reside in aconfinement structure that provides a current exposure (e.g., through aslot or series of openings in the confinement structure) approximating aC-shaped electrode. In this case the electrode itself may have a varietyof shapes, as its function will be determined by the shape of theconfinement structure, which essentially forms a virtual electrode. Theposition of the auxiliary electrode, in some embodiments, may includeany position about the periphery of the wafer, such as those disclosedin the US Patent Application Pub. No. 2010/0116672, titled “Method andApparatus for Electroplating” by Mayer et al. published May 13, 2010,which is herein incorporated by reference in its entirety. Thecontainment structure for the auxiliary electrode, when used, mayinclude a plurality of through-holes allowing for communication of theelectrode with the plating cell, such as those described in theProvisional U.S. Application No. 61/499,653, titled “PurgingMicro-Containments During Electroplating” filed Jul. 1, 2011 by Feng etal.

Methods and apparatus for aligning and varying the amount of current andthe sign of the current in time and space between the azimuthallyasymmetric electrodes and the selected azimuthal positions on the wafersubstrate, and for adjusting dwell times of selected azimuthal positionsof the wafer in the proximity of thief cathodes, are provided.

In the embodiments presented herein, it is important that the positionof the selected azimuthal region on the substrate (i.e., that regiontargeted for special treatment) be known prior to electroplating.Therefore, in the embodiments presented herein a selected azimuthalposition is registered prior to electroplating, e.g., with an opticalaligner. For example, a position of the notch on the wafer (selectedazimuthal position) can be measured by a notch aligner. Some positionand notch aligners use an optical measuring device, comprising aphotodiode array, which is capable of acquiring a shadow image of thesubstrate and store it in a memory file, e.g., in a digital linear file.The registration of the notch position is determined, and with thisknowledge, by computation relative to the notch, of the selectedazimuthal region for special treatment, allows controlling theorientation of this azimuthal position throughout the plating process,and synchronization of shields and/or auxiliary electrodes (positionand/or power applied) with a specific azimuthal region on the wafer, asdesired. In a typical electroplating process provided herein, theposition of a selected azimuthal portion of the substrate is known withrespect to the indexing notch position prior to electroplating andduring electroplating, allowing for orchestration of azimuthal currentcorrection throughout the plating process. As a specific example, thewafers may be notch aligned inside the Front Opening Unified Pod (FOUP)prior to being placed onto the plating tool. In another example, thewafers pass through a notch aligning device just prior to undergoingplating. In a third example, the notch alignment is done on a platingtool as a initial step in the sequence of subsequent plating and/ornon-plating operations (e.g. rinsing and chemical pretreatment, vacuumpretreating, surface pretreating, copper plating, nickel plating,lead-free solder plating, gold plating) wherein the change in theorientation of the wafer can be tracked as long as the operation in eachchamber does not lead to a loss of registry (such as slipping in a waferholding chuck).

In some embodiments, the methods and apparatus provided herein addresscorrections for both radial and azimuthal non-uniformity.

In some embodiments, radial plating uniformity control can be achievedthrough use of an ionically resistive ionically permeable element,positioned between the working electrode (the wafer substrate) and thecounter electrode (the anode) during plating, in order to shape theelectric field and control electrolyte flow characteristics. Forexample, an ionically resistive element having electrolyte-permeable 1-D(i.e., non-communicating) through-holes, where the element resides inclose proximity of the wafer substrate has been found to be highlyeffective in this regard. One example of such an ionically resistiveelement is described in U.S. non-provisional application Ser. No.12/291,356, entitled, “Method and Apparatus for Electroplating,” byJonathan Reid et al., filed on Nov. 7, 2008, which is incorporated byreference herein for all purposes. The ionically resistive ionicallypermeable element described therein substantially improves radialplating uniformity on thin resistive seed layers. It is particularlyuseful when employed in combination with a second (thief) cathode oranode configured to divert or supply a portion of current from near-edgeregion of the wafer. It is also compatible with potential-controlledwafer entry, which is, in some embodiments, a preferred wafer entryprocess. The ionically resistive ionically permeable element serves forachieving a nearly constant and uniform current source in the proximityof the wafer (cathode) and has been referred to as a virtual anode. Incontrast, an anode in the same close-proximity to the substrate would besignificantly less apt to supply a nearly constant current to the wafer,but rather, would support a constant potential at the anode metalsurface, thereby allowing the current to be greatest where the netresistance from the anode plane to the terminus (e.g. to peripheralcontact points on the wafer) is smaller. So while the ionicallyresistive ionically permeable element has been referred to as ahigh-resistance virtual anode (HRVA), this does not imply thatelectrochemically the two are interchangeable. While the HRVA iscertainly viewable as a “virtual current source”, i.e. it is a planefrom which the current is emanating, and therefore can be considered a“virtual anode” because it is a source of anodic current flow, it is therelatively high-ionic-resistance of the element (with respect to theelectrolyte) that leads to further advantageous, generally superiorwafer uniformity when compared to having a metallic anode located at thesame physical location. And of particular relevance to this disclosureis a preferred embodiment construct wherein a variable spacing, size anddensity of the 1-D HRVA holes in either the radial and/or the azimuthalarray of holes creates a highly controllable, non-uniform source ofcurrent at the periphery. This, combined with the registration of thewafer angular position (notch) and the dwell/rotation rate with angularposition, operates to correct for azimuthal non-uniformities in ananalagous manner to having a shield blocking the source of current froman anode below the wafer.

Two features of the HRVA are of particular importance: the placement ofHRVA in close proximity with respect to the wafer, and the fact thatthrough-holes in the HRVA are spatially and ionically isolated from eachother and do not form interconnecting channels within the body of HRVA.Such through-holes will be referred to as 1-D through-holes because theyextend in one dimension, often, but not necessarily, normal to theplated surface of the wafer (in some embodiment the 1-D holes are at anangle with respect to the wafer which is generally parallel to the HRVAfront surface). These through-holes are distinct from 3-D porousnetworks, where the channels extend in three dimensions and forminterconnecting pore structures. An example of a HRVA is a disc made ofan ionically resistive material, such as polyethylene, polypropylene,polyvinylidene difluoride (PVDF), polytetrafluoroethylene, polysulphone,polyvinyl chloride (PVC), polycarbonate, and the like, having betweenabout 6,000-12,000 1-D through-holes. The disc, in many embodiments, issubstantially coextensive with the wafer (e.g., has a diameter of about300 mm when used with a 300 mm wafer) and resides in close proximity ofthe wafer, e.g., just below the wafer in a wafer-facing-downelectroplating apparatus. Preferably, the plated surface of the waferresides within about 10 mm, more preferably within about 5 mm of theclosest HRVA surface.

The presence of a resistive but ionically permeable element close to thewafer substantially reduces the terminal effect and improves radialplating uniformity. It also simultaneously provides the ability to havea substantially spatially-uniform impinging flow of electrolyte directedupwards at the wafer surface by acting as a flow diffusing manifoldplate. Importantly, if the same element is placed farther from thewafer, the uniformity of ionic current and flow improvements becomesignificantly less pronounced or non-existent. Further, because 1-Dthrough-holes do not allow for lateral movement of ionic current orfluid motion within the HRVA, the center-to-edge current and flowmovements are blocked within the HRVA, leading to further improvement inradial plating uniformity.

Another important feature of the HRVA structure is the diameter orprincipal dimension of the through-holes and its relation to thedistance between the HRVA and the substrate. Preferably the diameter ofeach through-hole (or of majority of through-holes), should be no morethan the distance from the plated wafer surface to the closest surfaceof the HRVA. Thus, the diameter or principal dimension of the throughholes should not exceed 5 mm, when HRVA is placed within about 5 mm ofthe plated wafer surface.

Thus use of a HRVA as described above can address radial non-uniformity.In order to address azimuthal non-uniformity additional features andmethods are needed. Embodiments described herein include one or morecomponents of the plating apparatus that compensate for the azimuthalasymmetry on the wafer surface during plating. More specifically, theone or more components of the plating apparatus shape the electric fieldin such a way so as to compensate for the azimuthal asymmetry on thewafer surface and thus provide highly uniform azimuthal plating inaddition to highly uniform radial plating. “Azimuthal asymmetry” mayrefer to azimuthal non-uniformity in topography, the resultant platingcurrent non-uniformity that results, the resultant field variationscreated by such local topography, or combinations thereof.

It is noted that in some embodiments, the HRVA plate can be usedprimarily or exclusively as an electrolyte flow shaping element,regardless of whether it tailors radial deposition uniformity or not.Thus, for example, in TSV and WLP electroplating, where metal is beingdeposited at very high rates, uniform distribution of electrolyte flowis very important, while radial non-uniformity control may be lessnecessary. Therefore the HRVA plate can be referred to as both ionicallyresistive ionically permeable element, and as a flow shaping element,and can serve from a deposition-rate corrective prospective in eitheraltering the flow of ionic current, in altering the convective flow ofmaterial, or both.

Embodiments described herein address azimuthal non-uniformity usingcomponents of the plating apparatus that shape the field in such a wayas to compensate for azimuthal topographical variation on the waferduring plating. More specifically, the wafer and these field shapingcomponents are moved, in some embodiments, relative to one another insuch a way that the localized field or fields produced by the componentsare proximate to the azimuthally asymmetric topographical features forwhich they are intended to compensate and thus uniform azimuthal platingis achieved. In embodiments described herein, control of the waferrotation and/or shield rotation and/or the HRVA rotation and/orauxiliary electrode rotation can be accurately synchronized using one ormore rotational digital encoders. Additionally, the localized shapedfields produced by components described herein need not always beproximate the areas of the wafer with azimuthally asymmetric topography,that is, the localized fields may only spend a disproportionate amountof time (referred to as “dwell”) proximate these areas relative to otherportions of the wafer so that azimuthally uniform plating is achieved.This may be termed “azimuthal averaging.”

Since the methods described herein in some embodiments, involve one ormore of the wafer and/or shields rotating relative to one another, themethods are sometimes referred to as “rotationally variable shielding”(RVS), and the apparatus as containing rotationally variable shields(RVS's). The azimuthally asymmetric shields used herein may include anyof the azimuthally asymmetric shields described in the U.S. Pat. No.6,919,010 issued on Jul. 19, 2005 to Mayer et al., and titled “Uniformelectroplating of thin metal seeded wafers using rotationally asymmetricvariable anode correction”, in the U.S. Pat. No. 7,682,498 issued onMar. 23, 2010 to Mayer et al., titled “Rotationally asymmetric variableelectrode correction” and in U.S. Pat. No. 6,027,631 issued on Feb. 22,2000 to Broadbent et al., and titled Electroplating system with shieldsfor varying thickness profile of deposited layer”, which are all hereinincorporated by reference.

Below is a short description of some operative characteristics of RVSs.Generally, as in the description herein, the RVS shield is a dielectricelement that is located close to the wafer that serves to block lines ofcurrent from reaching the wafer from an anode position “below” (in thecase where the anode is below the wafer) for a period of time when aparticular portion of the wafer lies “above” the RVS shield. To be mosthighly effective, the RVS element should be positioned relatively closeto the wafer so that current cannot circumvent the shield, flowingaround the RVS element edges and into the bulk of the shielded area. Theimprint or influence of the RVS is therefore limited by the “proximityfocusing” of the element. To avoid significant smearing of the elementseffects, the element's arc length (about an azimuth) at a particulardistance from the center of rotation therefore should be several times(e.g. >3 times) the distance between the RVS shield and the wafersurface. For example, if the distance between the wafer and the RVSshield is 4 mm, the RVS shield would need to be about 12 mm in arclength to be highly effective. In designing a shield, in particular, fordesigning uniformity corrections at near the wafer center, thesecharacteristic ratios may no longer need be used, and so modificationsin the shape of the RVS as would be predicted by a “blocking model” maybe required to compensate for the ability of current to travel aroundthe RVS and significantly into the area behind the shield.

In some embodiments, the RVS shield is incorporated into the design of aHRVA plate. A “HRVA,” as used herein, is for convenience, because whenused in this particular set of operations, the porous plate does notnecessarily have to exhibit a relatively high resistance to the totalcell electrolytic solution resistance to be functional as a rotationallyvariable shielding element. As mentioned above, it can also be referredas a flow shaping element. The HRVA plate can serve many purposes, forexample, including but not limited to modifying the current distributionon the wafer, creating shearing flow between the rotation wafer and theplate, creating a high impinging flow up at the wafer surface, and flowturbulence. In some embodiments the HRVA plate is created by drilling alarge number of holes (e.g. 6000 holes 0.5 mm in diameter over anapproximately 300 mm diameter area) into a solid piece of dielectricmaterial (e.g. a 0.5 inches thick piece of plastic such aspolypropylene). With regards to the embodiments described herein, theRVS shield is then created by not drilling holes in the plate in aspatially regular pattern, but rather only into select areas and notinto other area, in order to create the various current blockingpatterns described herein as required by the RVS (as well as othertechniques for selectively blocking predrilled holes are describedbelow). In some embodiments, a select HRVA constructed with a particularholes pattern is used to create the shield pattern. In other embodimentsonly the RVS pattern is created in this manner, and peripheral extraholes in the HRVA can be blocked by placing shields of various sizes,angles, etc., allowing for modification of the shield performance as maybe needed from time to time or from wafer-pattern to wafer-pattern. TheHRVA having azimuthally asymmetric hole-free regions assumes a functionof an azimuthally asymmetric shield.

For the purposes of simplicity, the following description assumes thatthere is a single feature or region of the wafer that has azimuthalasymmetry, for example, a sector of a wafer has die and non-die areas,or for example, a wafer where a chord or notch is cut from the wafer.Embodiments described herein also include methods and apparatus toachieve high azimuthal plating uniformity where there is azimuthaltopographical variation, for example, in more than one area on thewafer, for example, where multiple dies are lithographed over most ofthe wafer's surface, and where there are non-die outlying areas near andaround the entire perimeter of the wafer surface. In such instances,components are configured and/or methods performed, to compensate forsuch azimuthal asymmetry, as will be apparent to one of ordinary skillin the art in light of this description.

Unidirectional Wafer Rotation

In one embodiment, the wafer is rotated in a single direction, forexample clockwise about an axis perpendicular to the surface of thewafer, and the components configured to produce a localized fieldproximate to the azimuthally asymmetric topographical features arevaried in synchronization with respect to the rotating wafer in order tocompensate for the azimuthal asymmetry and provide uniform azimuthalplating. Examples of this embodiment are described below. It is notedthat these described embodiments are illustrated as used in conjunctionwith a unidirectionally rotated wafer, but, more generally, can be alsoused where the wafer rotates bidirectionally (both clockwise andcounterclockwise) during electroplating and where the wafer rotates atconstant or variable speed (including both unidirectionally andbidirectionally).

Segmented Auxiliary Electrode

In some embodiments, a second electrode, a (thief) cathode or source(anode) or an anode/cathode, includes several segments, where each ofthe segments can be separately powered by a separate power supply orusing one power supply having multiple switches or channels adapted toindependently power segments of the second cathode. Specifically, in oneexample, segments of a second cathode are used for providing platingcurrent corrections at different azimuthal positions of the wafer as thewafer rotates. The current applied to any individual secondary electrodesegment at any point in time may be positive, negative, or zero, withthe sign and amount of current varying in time correlated andsynchronized with the wafer angular position at that time. As it hasbeen previously mentioned, any of the current, voltage, or a combinationof these may be controlled, in order to correlate power provided toelectrode (or a segment) with the rotation of the wafer.

In this multi-segmented electrode embodiment, the wafer substrate isfirst registered such that a position of a selected azimuthal portion onthe wafer is known, is secured in the substrate holder in theelectroplating apparatus such that its platable surface is immersed intoelectrolyte, and is rotated in the electroplating apparatus having astationary multi-segmented thief cathode or anode source or ananode/cathode, which is configured to divert or supply additionalcurrent from or to the wafer edge in the limited area of the waferperiphery associated with the location and azimuthal extent of theparticular electrode. The individual segments of the thief cathode orsecondary anode source are disposed about different azimuthal positions,and can be powered separately, such that different levels of current canbe applied to different segments of the thief cathode. The power appliedto the segments is synchronized with the rotation of the substrate insuch a manner that a selected portion of the substrate at a selectedazimuthal position will experience a different amount of plating currentdiverted by a thief (or donated by an auxiliary anode), than ananalogous portion (i.e. a portion of the average same arc length andsame average radial position) of the substrate at a different azimuthalposition. For example, a higher (or lower) level of thieving current maybe applied to those segments of the thief cathode, which are locatedproximate the selected azimuthal position.

This concept is illustrated in FIGS. 1A and 1B which show a schematicview of a wafer 101 having a missing die region 103 (selected azimuthalposition). Peripheral to the wafer are located four thief cathodesegments, 105, 107, 109, and 111, each electrically connected to its ownpower supply 113, 115, 117, and 119. One of ordinary skill in the artwould appreciate that one power supply with a plurality of channels canalso be used. For example, a single power supply with a combination ofswitches and/or current modulators could be used. In those embodiments,where an anode/cathode is used, the segments are connected to bipolarpower supplies. The thief electrode segments are located at differentazimuthal positions with respect to the wafer. The segment 105 isaligned with the missing die region and resides at 0° azimuth. Segments107, 109, and 111 reside at 90°, 180°, and 270° azimuthal positionsrespectively. As the wafer 101 rotates in the clockwise direction, themissing feature region 103 becomes aligned consecutively with thesegment 107, then with segment 109, with segment 111, and then againwith segment 105. FIG. 1B shows the same system as shown in FIG. 1A,with the wafer rotated by 90° such that the wafer flat 103 is alignedwith the thief segment 107.

Because current density at the missing die region will be different thanthe current density at other regions of the wafer, a different amount ofcurrent needs to be diverted from the missing die part as compared withthe other parts. Accordingly, in one embodiment, the thief cathodesegments are powered in concert with wafer rotation, such that a firstlevel of current is supplied to the segments aligned with the missingdie region, while a second level of current is supplied to the thiefsegments aligned with the other portions of the wafer.

For example, in a position shown in FIG. 1A, a first level of current,X, is supplied to the segment 105 aligned with the wafer flat 103, whilea second (different) level of current, Y, is supplied to each of thesegments 107, 109, and 111. As the wafer rotates 90° to a position shownin FIG. 1B, the first level of current, X, will be supplied to thesegment 107, now aligned with wafer flat 103, while the second level ofcurrent Y, is supplied to the segments 109, 111, and 105. By alternatingthe current supplied to the auxiliary electrodes segments in accordancewith wafer rotation, a correction for plating non-uniformity at circularand the chord region of the wafer is properly made. A controllerconnected to the power supplies and containing program instructions forcorrelating the power levels supplied to thief segments with waferrotation speed, can be used to orchestrate the process.

As it has been mentioned, this embodiment is not limited to the use of amulti-segmented thief cathode, but may also be used with amulti-segmented anode, or a multi-segmented anode/cathode. In aparticularly preferred embodiment, the current of each element may be ofan optimally determined waveform having a sequence of alternatingcurrent levels or signs during the period of wafer rotation. Forexample, by having a plating cell designed with an edge shield and/orHRVA that would create a generally thin deposit in regions of the waferwhich are not missing die or features, and designed to give a generallythick set of features in the missing die/feature region, current addingand removing “pulses” to the wafer can be applied to the wafer as itrotates. Then the sign of each of the segments of themulti-segmented-electrode will change from anodic (supplying peripheralanodic current) when the thin majority edge is proximate, and cathodic(removing peripheral anodic current) when the minority thick region(missing die/feature region) is aligned and proximate.

It is understood that the presentation shown in FIGS. 1A and 1B isschematic only. The auxiliary electrode segments are generally locatedoutside and around, or just under the wafer periphery, and when outsideand around the wafer, can be located below, at the same level, or abovethe wafer plane, either in the same plating chamber as the wafer or in adifferent plating chamber in ionic communication with the main platingchamber. Any appropriate arrangement of the segments can be used, aslong as the segments are aligned with different azimuthal positionsabout the wafer. The number of segments can vary depending on the needsof the process. In some embodiments between about 2-10 segments areused.

While the multi-segmented thief cathode is particularly useful with aHRVA disposed in close proximity of the wafer, this is a separateembodiment which can be used both independently and in combination withvarious plating apparatus features disclosed herein. In otherembodiments, which will later be illustrated with reference to FIGS.10A-10C, a second electrode (thief cathode or source anode oranode/cathode), is azimuthally asymmetric and has a unitary body. Forexample an electrode having a unitary body with a segment removed, forexample an annulus with a segment removed (also referred to as aC-shaped electrode), could be powered synchronously with the wafer. Inanother embodiment, an azimuthally asymmetric electrode (cathode oranode) is moved with the wafer at the same speed, synchronously with thewafer, so that the appropriate localized field configured to compensatefor the azimuthal non-uniformity remains registered with the area of thewafer for which it was designed to field compensate. Such auxiliaryelectrode may be segmented so that more than one area has azimuthalplating correction, for example, where the segments are arrangedappropriately on a support which rotates in sync with the wafer duringplating. Such apparatus and methods are within the scope of theinvention; however they may be more complex, for example, having moremoving parts than are necessary to accomplish the same end. Thisembodiment includes registering the position of a selected azimuthalposition prior to electroplating, providing the wafer substrate to theelectroplating apparatus having an azimuthally asymmetric (e.g.,C-shaped) or multi-segmented electrode (cathode, and/or anode) (havingsegments disposed at different azimuthal positions) and rotating boththe substrate and the auxiliary electrode, such that the selectedportion of the substrate at a selected azimuthal position dwells in theproximity of the azimuthally asymmetric electrode or in the proximity ofa segment of the multi-segmented electrode for a different amount oftime than an analogous portion at a different azimuthal position. Insome embodiments, both the auxiliary electrode (azimuthally asymmetricor multi-segmented) are rotated at the same speed as the wafer substratesuch that selected azimuthal position of the wafer is aligned with theasymmetric electrode or a segment of the electrode, such that it iscloser (or farther away) to that electrode or the segment than ananalogous portion of a substrate at a different azimuthal (angular)position. In another embodiment, a single “C” shaped electrode is fixedand only the wafer rotates, with the applied current to the “C shapedelectrode varying during the wafer rotation cycle, for example fromanodic to cathodic currents, or to different levels of anodic, ordifferent levels of cathodic current. When the electrode is locatedcloser to the selected portion of the substrate a greater amount ofplating current is diverted towards the thief (or donated by the anode),and this can mitigate current crowding, and unnecessarily thick plating,in selected areas.

Rotating HRVA Having Non-Uniform Distribution of 1D Through-Holes

In another embodiment, the plating uniformity on azimuthallyasymmetrical wafers can be adjusted by using a rotating asymmetricalHRVA. The asymmetrical HRVA can have a portion that has a different holedistribution pattern from the main portion, or a portion that is cutoff, or a portion without holes altogether. The rotating HRVA is alignedwith the rotating wafer such that a distinct portion of the wafer isaligned with a distinct portion of the HRVA. For example, a wafer havinga wafer flat region or missing die can be rotated at the same speed asthe rotating HRVA such that a region of HRVA having a non-uniform holedistribution (e.g., lower density of holes) is aligned with the waferflat region during rotation.

FIGS. 2A and 2B show a top view of a rotating HRVA 201 having a region203, where distribution of holes is different from the rest of the HRVA(thus an “asymmetrical HRVA”). In some embodiments the region 203 may beabsent (cut off to a chord) or it can be solid without holes. In someembodiments (not illustrated) the region with non-uniform distributionof holes is wedge-shaped or is otherwise azimuthally asymmetric. Therotation of the HRVA is aligned with the rotation of the wafer (notshown), such that the region 203 is aligned with the wafer flat ormissing die region, as the wafer rotates. FIG. 2B shows HRVA havingnonuniform region 203 upon rotation to 90°. A controller which includesprogram instructions for synchronizing wafer rotation and HRVA rotationwill be connected with the HRVA and the wafer in some embodiments. Oneembodiment is any embodiment described herein where a symmetrical HRVAis described, but substituting an asymmetrical HRVA to add an additionalplating profile shaping element to the apparatus or method.

This embodiment can be used separately or in combination with theauxiliary electrode and other features disclosed herein. In someembodiments using rotating asymmetrical HRVA, the HRVA does not need tobe positioned in close proximity of the wafer.

Stationary HRVA with a Rotating Shield

In another embodiment, the plating uniformity control for an azimuthallyasymmetrical wafer is achieved by using a rotating shield positionedabove or below the HRVA. In some embodiments, the rotating shield ispositioned in close proximity of the substrate (e.g., with a distance tothe platable surface of the substrate within about 0.1 of thesubstrate's radius, such as within about 0.2 of the substrate's radius,and, preferably, within about 4 mm). The shield is configured to eclipsethe HRVA holes and is shaped such as to compensate for non-uniformity ofcurrent density distribution at the regions of the wafer havingazimuthally asymmetric topographical features. The shield is alignedwith the wafer flat and rotates at the same speed as the wafer,providing a continuous adjustment to current density experienced by theregion where azimuthal surface variation exists. The shield can have avariety of shapes, such as a wedge shape, a gingko leaf shape, abat-wing shape, etc. The synchronization of the shield and waferrotating speeds can be done using a controller having programinstructions for synchronization. More generally, the HRVA is notnecessary in some embodiments, and the rotating azimuthally asymmetricshield is aligned with a selected portion of the substrate at a selectedazimuthal position and is rotated with the substrate at the same speed,such that the selected portion of the substrate at a selected azimuthalposition dwells in the shielded area for a different amount of time thanan analogous portion at a different azimuthal position.

The embodiments described above are within the scope of this invention,but may be regarded as having more moving parts than are necessary toachieve azimuthal plating uniformity. By rotating the waferbidirectionally or at variable speed, many of the implementationdifficulties associated with moving parts can be avoided.

Bidirectional Wafer Rotation

In another embodiment, the components, configured to produce a localizedfield proximate to the azimuthally asymmetric topographical features,are fixed and the wafer is rotated bidirectionally, for exampleclockwise and counterclockwise about an axis perpendicular to thesurface of the wafer, such that the synchronization between the waferand the field shaping components is achieved and thus the azimuthalasymmetry on the wafer is compensated for and uniform azimuthal platingis achieved. The components include stationary azimuthally asymmetricshields (including a stationary HRVA with an azimuthally asymmetricdistribution of holes), azimuthally asymmetric auxiliary electrodes(thief cathodes, anodes, and anode/cathodes) and multi-segmentedauxiliary electrodes, having segments distributed at various azimuthalpositions. Bidirectional rotation can be used such as to adjust a dwelltime of a selected portion of the substrate at a selected azimuthalposition in a shielded area, or in an area proximate to an auxiliaryelectrode (or an electrode segment) such that this dwell time isdifferent from a dwell time of an analogous portion of a substrate at adifferent azimuthal position (having the same average arc length andsame average radial position). For example, if the wafer is rotatedclockwise and counterclockwise to a different degree, it will spend moretime at certain azimuthal positions, relative to others. These positionsmay be selected such as to correspond to azimuthal positions that areshielded or that are proximate to an azimuthally asymmetric thief or athief segment. For example, if the wafer is rotated clockwise by 360degrees and counterclockwise by 90 degrees, it will spend more time inthe sector between 270-360 degrees. Furthermore, bidirectional rotationcan tends to reduce or eliminate any particular directional wafer flowfield bias.

Segmented Auxiliary Electrode (Thief Cathode/Source Anode orAnode/Cathode) or an Azimuthally Asymmetric Auxiliary Electrode withBidirectional Wafer Movement.

As described above, when a segmented thief cathode or an azimuthallyasymmetric thief cathode, which is adapted for diverting a portion ofcurrent from the edge of the wafer, is used to compensate for azimuthalnon-uniformities on a wafer, and when the wafer is rotatedunidirectionally, one way to achieve azimuthal plating uniformity is tomove the thief cathode synchronously with the wafer so that theappropriate localized field configured to compensate for the azimuthalnon-uniformity remains registered with the selected area of the waferfor which it was designed to compensate. Such thief cathodes may besegmented so that more than one area has azimuthal plating correction,for example, where the segments are arranged appropriately on a supportwhich rotates in sync with the wafer during plating.

If the wafer is moved bidirectionally in a manner described above, thenthe secondary thief cathode can remain stationary, as the selectedazimuthal position of the wafer, e.g., a missing die region will have adifferent dwell time in the proximity of the auxiliary electrode or itssegment than a different azimuthal position of the wafer. This obviatesa number of mechanical complexities. One embodiment is a platingapparatus configured for bidirectional movement of a wafer, a segmentedsecondary thief cathode configured to divert the plating current,wherein the apparatus is configured to adjust the field to compensatefor azimuthal non-uniformities on the wafer. In this embodiment in thebidirectional rotation, the wafer rotates clockwise and counterclockwiseto a different degree (or rotates to the same degree without making afull rotation, e.g., over selected arc length), such that the selectedportion of the wafer at a selected azimuthal position dwells inproximity of a thief cathode segment for a different time (e.g., longer)than an analogous portion of the substrate at a different azimuthalposition. In some embodiments, the selected segment of the cathode ispowered differently from other segments (e.g., has a different level ofcurrent applied or different polarity from other segments. Anotherembodiment is a method of plating including rotating the waferbidirectionally, relative to a secondary segmented thief cathode, so asto compensate for azimuthal non-uniformities on the wafer duringplating. Although this embodiment was illustrated with a thief cathodediverting current, it can also be used with an auxiliary multi-segmentedanode or anode/cathode. In these embodiments the HRVA may or may not bepresent and may or may not be rotated during plating. Typically, but notnecessarily, the HRVA is a symmetrical HRVA as opposed to anunsymmetrical HRVA as described above. The secondary auxiliaryelectrodes operate to manipulate the field as described herein, but arenot moved during plating.

Azimuthally Asymmetric Shields

In some embodiments, the apparatus is configured for rotating the waferbidirectionally and the apparatus includes one or more stationaryazimuthally asymmetric shields, configured for restricting platingcurrent in the proximity of the substrate. The shields may be usedindependent of the HRVA, and may be placed above or below the HRVA plateblocking the HRVA holes, or the shield may itself be the HRVA havingazimuthally asymmetric distribution of through-holes. In someembodiments the bidirectional rotation is adjusted such that a selectedportion of the substrate at a selected azimuthal position (e.g.,proximate to a notch or a missing die) dwells in the shielded area for adifferent time than an analogous portion of the substrate at a differentazimuthal position. This may be accomplished, for example, if clockwiseand counterclockwise rotations are performed to different degrees, suchas to create a longer dwell time of a selected azimuthal portion of thewafer in a certain shielded position. Below are non-limiting examples ofvarious implementations of azimuthally asymmetric shielding.

Stationary HRVA with a Segmented or Irregular Annular Shield:

In one embodiment, the plating uniformity control for an azimuthallyasymmetrical wafer is achieved by using a stationary HRVA with anattached azimuthally asymmetric shield, where the azimuthally asymmetricshield is an annular shield which has one or more segments removedand/or one or more areas disposed azimuthally about the annulus thatimpart azimuthal asymmetry to the annular shield. The wafer is rotatedbidirectionally, for example one or more rotations clockwise and thenone or more rotations counter clockwise, such that the wafer areas inneed of azimuthal plating compensation are azimuthally averaged, thatis, positioned over the appropriate segments and/or aforementioned areasappropriately to provide field shaping for the azimuthally uniformplating to occur. The adjustment of the dwell time of a specificazimuthal position over the shield via adjustment of wafer rotatingspeeds and/or directions can be done using a controller having programinstructions for synchronization.

In one embodiment, symmetrical HRVA is used in combination with anannular shield that attaches to the HRVA. In one embodiment, the annularshield (or spacer) is affixed to the HRVA, and the annular shield has asector removed, a feature or area that imparts asymmetry to the annulus.Typically, when bidirectional wafer rotation is employed, the HRVA andattached shield are not moved. In one embodiment, the annular shield hasa sector removed, as depicted in FIG. 3A.

Referring to FIG. 3A, an annular shield, 300, is mounted to asymmetrical HRVA, 302, as indicated by the heavy downward arrow. Thebottom assembly, 306, shows the segmented shield in contact with theHRVA. In certain embodiments, since there is an impinging flow ofelectrolyte from the HRVA onto the wafer surface, and segmented shieldssuch as 300 are commonly, but not necessarily, positioned proximate thewafer, the shield imparts lateral shearing forces at the wafer's platingface during plating, and particularly at the central axis of rotation onthe plating face. This shearing is believed to reduce or eliminate thenon-uniformity in deposition rate observed at the center of the wafer,particularly at higher plating rates. Thus segmented annular shields mayalso be called azimuthally non-uniform flow diverter (which can bethought of as a type of flow constrictor, i.e. constricting the majorityof the electrolyte flow deflected from the wafer surface through thesegmented region). In some applications, this type of flow diverter isused in applications where high plating rates are desired, for examplewafer level packaging (WLP) applications. One example of such anapplication is described in U.S. provisional application, Ser. No.61/374,911, entitled, “High Flow Rate Processing for Wafer LevelPackaging” by Steven T. Mayer et al., filed on Aug. 18, 2010, which isincorporated by reference herein for all purposes.

Annular shield 300 can be attached to or proximate the circumference ofthe flow shaping plate and extending toward the rotating work piece. Insome embodiments depicted here, the top surface of the edge element ofthe shield provides a very small gap (e.g., about 0.1 to 0.5 mm) betweenthe bottom of the wafer holder and flow diverter over the majority ofthe region between a substrate holder periphery and the top of the edgeelement. Outside this region (between about 30 to 120 degrees arc),there is a gap in the edge element that provides a relatively lowresistance path for electrolyte to flow out of the nearly closedchamber. In other embodiments, where there is no segment removed fromthe annular shield, i.e., there is an area that imparts azimuthalasymmetry, the shield may or may not be as close to the wafer dependingupon, for example, the amount of desired electrolyte flow.

FIG. 3A depicts how segmented annular shield 300 combines with HRVA 302to form assembly 306. Annular shield 300 can be attached, for example,using screws and the like (not shown) or assembly 306 can be a unitarybody milled from, for example, a block of material. Assembly 306 ispositioned in close proximity to the substrate to be plated. In thisway, a confined space or pseudo chamber is formed between the wafer andthe flow shaping plate wherein the majority of the electrolyte impingingon the wafer surface exits through the slotted portion of 300. DimensionA, which may be defined as an angle or a linear dimension for a ring ofdefined radius, can be varied to allow more or less field changing area(and in this example flow through the slot) and dimension B can bevaried to create a larger or smaller volume in the aforementioned pseudochamber.

FIG. 3B is a cross sectional depiction of assembly 306 positioned inclose proximity to a wafer holder assembly 301, which holds wafer 345and can rotate the wafer bidirectionally during plating as indicated bythe curved arrows at the top of the figure. In certain embodiments, adimension C, which is a gap between the top of spacer 300 and the bottomof assembly 301, is on the order of about 0.1 to 0.5 mm, in anotherembodiment about 0.2 to 0.4 mm.

During plating, since the shield shapes the field differently in thesector defined by the cut out segment, the wafer is rotated back andforth, under the appropriate timing and synchronization with the shield,in order to achieve uniform azimuthal plating in the areas on the waferwith azimuthal non-uniformity.

In some embodiments the shield having an annular shape with a removedsector is not affixed to the HRVA but is rotated during electroplating,preferably at a speed that is different than the speed of the wafer,which helps optimize the flow of electrolyte in the proximity of thewafer.

As discussed, the annular shield need not be segmented. For example, itmay include a portion that imparts azimuthal asymmetry (in oneembodiment, the shield includes both at least one segmented portion andat least one portion that imparts azimuthal asymmetry). FIG. 4 depicts anumber of exemplary annular shields, including shield 300 and 400-475.In FIG. 4, the annular shields are depicted from a top view as attachedatop a symmetrical HRVA. Shields 400-475 are shields having a portion(area) that departs from annularity, that is, that imparts anazimuthally asymmetric field. That is, along a circle or annulus whichincludes that portion of the shield that departs from regularannularity, there is not a uniform plating field across the entirecircle or annulus.

It is important to note that although shield 300 is depicted as havinguniform thickness (dimension B as depicted in FIG. 3A) this is notnecessary. In one embodiment, the shield thickness varies. For example,the shields, 400-475, in FIG. 4A may be tapered in thickness. Forexample, referring to shield 405, in one embodiment the shield is ofuniform thickness. In another embodiment, the shield is tapered from thecenter portion of the shield to the outer portion, for example, thinnerat the center portions and becoming thicker toward the outer perimeteralong radius D. This thickness variation may be desired for efficientelectrolyte flow, for example from the center of the wafer outwards.This is analogous to the flow imparted by the segmented annular shield,300. This tapering can be from the inner to out portions along theentire annulus as well, not only the irregular portion of the annulus.

The shape of the portion of the annular shield (or independent shielddescribed herein) may be tailored to accommodate not only azimuthalplating non-uniformity but also radial non-uniformity. Referring to FIG.4B, for example, if there is a radial plating profile that is concave(as depicted in the graphical representations at the top left of FIG.4B) then the shield or portion of the annular shield that extends past(interior to) the regular annular portion of the shield may be shaped tocompensate for the concave radial plating profile. In this example,shield 480 a, is thinner towards the center of the HRVA 302 so that thecenter portion of the wafer, when passing over the shield, will haveless shielding and therefore more plating than outer portions thatencounter more shield area and thus less plating. In another example,where there is a convex plating profile, the shield (or portion ofannular shield) 480 b is shape so that there is less shielding towardthe perimeter of the wafer and more toward the center of the wafer.Asymmetric shield portions, for example as depicted in FIG. 4A, forexample in shields 440 and 445, as opposed to shields 400-435, and450-475 which are symmetric about a radius that bifurcates that portionof the shield that varies from annularity, may be desired depending uponthe azimuthal non-uniformity on the wafer and the rotation sequence ofthe wafer during plating. Thus, as depicted in shields 400-475, the areaof the portion of the annular shield that deviates from annularity maybe symmetric or not, depending upon the plating desired and theazimuthal asymmetry on the wafer to be plated.

As described, these non-uniformities in the field created by the variouscombinations of shielding and thieving described herein are exploited bycombining plating time and synchronization with or without theasymmetric portion of the field to compensate for azimuthalnon-uniformities on the wafer surface and achieve uniform azimuthalplating. In the embodiments described in this section, bidirectionalwafer rotation is used in combination with the shields described. Thetiming and synchronization will depend on, among other factors, theazimuthal non-uniformities on the wafer, the shield configuration, theamount of plating desired, the rate of plating, and the like. Thesynchronization of the shield features with certain areas of the wafer,wafer rotation speeds and rotation direction can be done using acontroller having program instructions for synchronization. Since theareas of the wafer with azimuthal non-uniformities wafer will spend acertain period of time over (or synchronized with) certain features ofthe shield, the described methods for obtaining azimuthal platinguniformity are sometimes referred to as “dwell shielding” methods. Toobtain a particular “dwell” over a shield, the wafer may be rotated at acertain rotation rate or speed (vs a rate over a non-shielded area), theshield may be wider, the wafer rotated a certain arc to ensure dwelltime, and combinations of these.

Stationary HRVA with a Segmented or Irregular Annular Shield and One orMore Additional Fixed Shields

In another embodiment, the plating uniformity control for an azimuthallyasymmetrical wafer is achieved by using an annular shield as describedin the previous section, for example a segmented shield attached to asymmetrical HRVA, in addition to one or more fixed shields in betweenthe annular shield and the wafer. The one or more fixed shields areconfigured to eclipse the HRVA holes and are shaped such as tocompensate, along with bidirectional rotation of the wafer and thesegmented annular shield, for non-uniformity of current densitydistribution at the regions of the wafer having azimuthally asymmetrictopographical features (and to compensate for radial non-uniformity).

FIG. 5A depicts annular segmented shield, 300, as described above, on asymmetrical HRVA, 302. The angle, Ω, in this example 90°, defines thecut out segment and, as described above, along with the proximity to thewafer defines not only field shaping about the annulus of the waferregistered with the shield during plating, but also electrolyte flowabout the wafer surface. The number of fixed shields and shape dependupon the wafer's azimuthal non-uniformities, the radial non-uniformityto be overcome, etc.

In one embodiment, the number of fixed shields, N, used in conjunctionwith shield 300 is defined by a formula, N=360°/Ω. For example, when Ωis 90° as in FIG. 5A, then N would be four. FIG. 5B depicts annularshield 300 with four fixed shields, 500 a-d, arranged in a regularpattern about the HRVA 302. In this example, shields 500 a-d are shapedto compensate for what would otherwise be a concave radial platingprofile (e.g., see FIG. 4B and associated description). The shape ofeach shield can vary independently in a given apparatus and/or theshields need not be arranged in a regular pattern about the HRVA. In oneembodiment, whatever their shape, the shields are arranged in a regularpattern as depicted in FIG. 5B, that is, where one shield is centered inthe open portion of the annular shield (in this example shield 500 doccupies that position). It is important to note that the embodimentdescribed using a segmented annular shield with one or more additionalfixed shields, for example as depicted in FIG. 5B, can be implementedwith, for example as depicted in FIG. 5C, an annular shield havingportions that protrude into the same space as shields 500 a-c, alongwith a separate shield 500 d. In another example, as depicted in FIG.5D, a single shield, 500 f is used. Shield 500 f has a unitary body, forexample milled out of a solid polymer or pressure molded. In thisexample, the portion of shield 500 f as indicated “E” is thinner thanthe thickness, B, of the remainder of the shield in order to allowelectrolyte flow as described above in relation to the segmented annularshield. The sub-portion of portion E of shield 500 f that is analogousto separate shield 500 d (as depicted in FIG. 5C) can also be, forexample, the same thickness B as the remainder of the shield, asdepicted in the bottom most portion of FIG. 5D. In this embodiment, whenthe wafer is positioned as described in relation to FIG. 2B, there areessentially two “higher flow” outlets for electrolyte to exit thepseudo-chamber formed when the wafer holder assembly is proximate theHRVA with shields. Of course, as described in relation to FIG. 4A, theportions of shield 400 f that correspond to individual shields 500 a-din FIG. 5B can be tapered, for example, thinner along dimension B in thecenter and becoming thicker toward the perimeter of the shield.

There are advantages to both having separate shields as depicted inFIGS. 4A and 4B, and having a single shield as in FIG. 5D. For example,having separate shields as described in relation to FIG. 5B allows oneto switch out shields 500 a-d, without having to change the annularshield 300. Also, the shields 500 a-d are mounted between the annularshield and the wafer, so there is corresponding support structure toaccomplish this. As well, when maximum flow through the segment area isdesired, having separate shields above the annular shield aids thisflow. A single shield, for example as described in relation to FIG. 5D,can be more simple to install, manufacture and operate due to lessparts, for example, support for the separate shields 500 a-d.

It is also important to note that the shields described thus far inrelation to a HRVA are described in terms of additional components, thatis, separate from the HRVA. This need not be so. For example, FIG. 5Edepicts a HRVA, 550, (analogous to that described in relation to FIGS.2A and 2B) where portions of the HRVA have less flow holes, or in thisexample, no flow holes, areas 560, and in this example, a single area,570, that does have the 1-D through holes. In this embodiment, theshielding is produced by the lack of holes in certain areas of the HRVA.Of course, the aforementioned electrolyte flow characteristics will bedifferent when the shielding components, as in HRVA 550, have novertical element, that is, thickness B. In another embodiment, asdepicted in FIG. 5F, the analogous areas, 560 a, not only have nothrough holes but are also raised, for example to height B, above thesurface of the HRVA, 570, having the holes. In the examples described inrelation to FIGS. 4E and 4F, either the through holes are formedselectively in the HRVA disk to form the pattern shown, or, in anotherexample, the through holes are made through the entire structure andthen selectively blocked, for example, in areas 560 and 560 a. Thelatter embodiment has the advantage of using existing drilled materialsand, for example, using screen printing to block the holes of interest.In another embodiment, the holes to be sealed are melted shut using aniron that is shaped in the pattern desired, or for example, moved aboutthe surface of the HRVA to melt shut the desired holes. The holes may bemelted shut in any number of ways including, using a conductive heatsource a convective heat source, an inductive heat source and aradiative heat source.

During plating, the wafer is rotated, for example bidirectionally, overthe HRVA and shields in order to obtain uniform plating both radiallyand azimuthally. For example, referring to the shield arrangements inany of FIGS. 5B-F, during plating, in one embodiment, the wafer isrotated bidirectionally about arcs of about 270°. For example, referringto FIG. 6, which depicts HRVA 580 of FIG. 5F, aspects of a platingprocess are described. A wafer, 600, which has a registration notch,605, is positioned over HRVA 580. The electrolyte flow passes throughHRVA 580 and impinges on the surface of wafer 600. For convenience,wafer 600 is depicted as an outline only so that the relativepositioning of wafer 600 and HRVA 580 can be seen, and wafer 600 isdepicted as having a smaller diameter than HRVA 580. The registrationnotch is proximate the area that needs the least amount of edgeshielding, as imparted by the annular portion of the shield elements,therefore as depicted in the left-hand portion of FIG. 6, the notch isstarted at the leading edge of the opening (segment) in the annularshield and the wafer is rotated 270° clockwise so that notch 605 ends upat the other edge of the open segment of the shield. In this way, theareas on the wafer adjacent to the notch, those requiring less edgeshielding, get more exposure to the field and thus more plating. Sincethe wafer is rotated 270°, each point on the wafer passes by threeinterior shield areas, represented by, for example, shields 500 a-d inFIG. 5B. In one embodiment the wafer is rotated in this way,bidirectionally, one or more times for each direction, clockwise andcounter clockwise, until the desired plating is achieved. As described,any number of combinations of annular shield (thickness, width andheight, segmented or not) and additional “interior” shield elements, forexample shields 500 a-d (thickness, width and shape can vary dependingupon the needs) can be used to tailor the plating uniformity bothradially and azimuthally.

Plating with Variable Rotation Wafer Speed

It is important to note that although the embodiments described aboveare in terms of unidirectional or bidirectional wafer rotation where therotation is a portion of a full 360 degrees rotation, azimuthalcorrections can also be performed by using variable speed wafer rotationThat is, if a wafer is rotated at a certain angular speed, R1, over agiven area, for example a holed area of the HRVA, and then rotated at adifferent angular speed, R2, over another area, for example a shieldedarea, the similar results can be obtained. That is, varying the rotationspeed during any individual full rotation is one way to adjust andobtain azimuthal variable amounts of time-averaged shielding to whichthe wafer is exposed. One embodiment, is any of the above describedembodiments, where the wafer speed is varied during each rotation, oralternatively, the speed may be varied during a single rotation or insome rotations and not others. Also, the wafer speed may be varied onlywhile spinning in one direction of rotation (e.g. clockwise) and not theother direction (e.g. counterclockwise), or it may be varied in bothrotational directions. One embodiment is any embodiment described inrelation to bidirectional wafer rotation, but using eitherunidirectional rotation where the rotation speed is varied during one ormore single rotations or a bidirectional rotation where the rotationspeed is varied.

These processes are illustrated by the process flow diagrams shown inFIG. 7 and FIG. 8. The first process is implemented in an apparatushaving one or more azimuthally asymmetric shields in the proximity ofthe substrate. Examples of shields include shields positioned above theHRVA, below the HRVA, or in the absence of the HRVA. In some embodimentsthe azimuthally asymmetric shield is a HRVA with an azimuthallyasymmetric distribution of holes. The process starts in operation 701 byregistering a selected azimuthal position on the wafer. For exampleazimuthal position of a notch may be registered by an optical alignerand recorded in the memory. In operation 703, the substrate is providedinto the substrate holder and is immersed into electrolyte. In operation705 the substrate is being plated, while being rotated at a first speedwhen the selected portion of the substrate is not in the shielded area.In operation 707, the substrate is rotated at a different speed, whenthe selected portion of the substrate passes through the shielded area.Thus, one full rotation of the wafer includes a period of rotation at afirst speed, and a period of rotation at a different speed, where theperiod of rotation at the second speed occurs at least partially whenthe selected portion of the substrate passes through the shielded area.As it was previously mentioned, the shields are preferably disposed inclose proximity to the substrate, such as within about 4 mm of theplatable surface, or within a distance that is equal or less to 0.1 ofthe substrate's radius. The variable speed rotations can then berepeated as necessary. For example, one full rotation may include aperiod of rotation at 20 rpm or more followed by a period of rotation at10 rpm or less, where plating includes at least 5 full variable-speedrotations. In one example, one full rotation of the wafer includes aperiod of rotation at about 40 rpm, when the selected portion of thewafer is not shielded, followed by a period of rotation at about 1 rpmfor about 10-15 degrees while the selected portion of the wafer passesthrough the shielded area. Plating may include at least about 10, suchas at least about 20 variable-speed rotations. It is understood that notnecessarily all rotations in electroplating are variable speed. Forexample, the plating process can include both constant-speed fullrotations and variable speed full rotations. Further, variable speedrotation can be implemented both during unidirectional and bidirectionalrotation in the electroplating process.

FIG. 8 illustrates a process flow diagram for plating in an apparatushaving an azimuthally asymmetric thief (e.g., a C-shaped thief) or amulti-segmented thief cathode. The process starts in 801 by registeringthe desired azimuthal position with an optical aligner. In 803, thesubstrate is placed into the wafer holder and is immersed in theelectrolyte. In 805, plating is performed while the wafer is rotated ata first speed, when the selected portion of the substrate at theselected azimuthal position is in the proximity of the azimuthallyasymmetric thief cathode or in the proximity of a segment of amulti-segmented cathode. In 807, the speed of rotation is changed (thewafer is slowed down or accelerated), when the selected area is not inthe proximity of the thief. Thus, in one full rotation, the waferrotates for a period of time at a first speed, when the selected area isin the proximity of a thief or a thief segment, and for a period of timeat a different speed, when the selected area is further away from thethief. Variable-speed rotation may be repeated for as many cycles asnecessary, e.g., at least 10 cycles.

It is understood that in some embodiments, where multiple shields and/ormultiple thief segments are contained in the apparatus, and/or where thewafer contains multiple selected areas where azimuthal uniformity needsto be corrected, one full rotation of the wafer may include multipleperiods of alternating slower and faster rotation, such as to registerthe required shields and/or thieves with all the necessary selectedazimuthal portions.

It is also noted that both bidirectional rotation and variable speedrotation uniformity correction methods can be characterized by thecapacity to provide different dwell times for a selected portion of asubstrate at a selected azimuthal position relative to dwell times of ananalogous portion of the substrate at a different azimuthal positions,wherein the dwell times refer to dwell of the selected portion in ashielded area on in a proximity of a thief cathode (or its segment). Asit has been previously mentioned, these embodiments may be also usedwith other types of auxiliary electrodes, such as auxiliary azimuthallyasymmetric anodes, and anode/cathodes, as well as multi-segmented anodesand anode/cathodes.

Patterning Method/Apparatus:

A schematic simplified cross-sectional view of an electroplatingapparatus, in accordance with one exemplary embodiment presented herein,is shown in FIG. 9. This non-limiting example illustrates an apparatuswith both an azimuthally asymmetric thief cathode (which, in otherembodiments, can be an anode or anode/cathode) and an azimuthallyasymmetric shield located above the HRVA. It is understood that in otherembodiments, the plating cell may have different components, or somecomponents may be absent, e.g., HRVA may be absent, and/or the apparatusmay contain a shield without the thief, or a thief without the shield.As depicted in FIG. 9, plating apparatus 901 includes a plating cell,903, which houses an anode 905. The anode may be an active anode (i.e.an anode which includes a metal that is being plated, such as copper ortin) or an inert anode. In this example, electrolyte 907, which includesions of platable metal, and an acid is flowed into cell 903 throughanode 905 and the electrolyte passes through a flow shaping element 909(also known as a HRVA, or an ionically resistive ionically permeableelement) having vertically oriented (non-intersecting) through holesthrough which electrolyte flows and then impinges on wafer 911 which isheld in, positioned and moved by, wafer holder 913. In the depictedexample the wafer holder is configured for bidirectionally rotating thewafer, and may also be configured for rotating the wafer at variablespeeds. The impinging flow of electrolyte is depicted by verticalarrows, which illustrate electrolyte flowing through the channels of theflow-shaping element 909, upward to the wafer 911. An azimuthallyasymmetric thief cathode 915 (e.g., a C-shaped thief residing about theportion of the wafer perimeter) resides over the flow shaping element909. More generally, the thief may reside anywhere in ioniccommunication with an electrolyte (e.g., within the plating bath or in aseparate chamber). The thief cathode 915 is connected to a negativeterminal of a power supply (not shown) and is configured to divert ioniccurrent from the wafer substrate. In addition, an azimuthally asymmetricshield 917 (e.g., a wedge-shaped shield) is position over the flowshaping element 909 in the proximity of the wafer substrate.

Preferably, in order to optimally control the uniformity, both the flowshaping element and the shield are positioned in close proximity to thesubstrate. In some embodiments the distance from a bottom surface of thesubstrate holder during electroplating and the top surface of the flowshaping element is between about 1 and 5 mm. The shield 917 preferablyresides within about 4 mm of the bottom surface of the substrate holder.

In some embodiments the flow shaping element is between about 5 mm andabout 10 mm thick and the substrate-facing surface of the flow shapingelement is separated from the plating face of the substrate by adistance of about 10 millimeters or less, more preferably by a distanceof about 5 millimeters or less during electroplating. In someembodiments, the flow shaping element is a disk having between about6,000-12,000 channels.

The wafer 911 typically has a plurality of electrical contacts made to aperiphery of the wafer, and is electrically connected to a negativeterminus of a power supply (not shown), such that the wafer, having aconductive layer thereon, serves as a cathode during electroplating. Thepositive terminus of the power supply is electrically connected to theanode 905. When potential difference is applied, an ionic current, whichmoves ions of platable metal and protons to the wafer surface, results.The ions of metal are reduced at the wafer surface, forming a layer ofelectroplated metal on the surface of the substrate. The uniformity ofplated layers depends on distribution of the plating field in theproximity of the substrate, which in turn, can be adjusted by shieldingwith the azimuthally asymmetric shield 917, and current diversion withthe azimuthally asymmetric thief 915, using methods provided herein.

A controller 919, electrically connected to the components of theelectroplating apparatus 901 includes program instructions, specifyingnecessary parameters for electroplating, such as levels of currentapplied to the wafer and the thief, parameters related to delivery ofelectrolyte to the plating bath, and speeds of rotation of the substrateand direction of rotation. The controller 919 includes programinstructions for performing all methods described herein, such asregistering the selected azimuthal position of the wafer such that itdwells differently in the shielded area or in the proximity of the thiefin comparison with an analogous region of the wafer at a differentazimuthal position. The controller will typically include one or morememory devices and one or more processors. The processor may include aCPU or computer, analog and/or digital input/output connections, steppermotor controller boards, etc.

In certain embodiments, the controller controls all of the activities ofthe deposition apparatus. The system controller executes system controlsoftware including sets of program instructions for controlling waferrotation speeds, registration of azimuthal position, etc.

Typically there will be a user interface associated with controller. Theuser interface may include a display screen, graphical software displaysof the apparatus and/or process conditions, and user input devices suchas pointing devices, keyboards, touch screens, microphones, etc.

The computer program code for controlling the deposition processes canbe written in any conventional computer readable programming language:for example, assembly language, C, C++, or others. Compiled object codeor script is executed by the processor to perform the tasks identifiedin the program.

It is understood that the depiction shown in FIG. 9 is a simplifiedscheme of one embodiment, which does not show all of the details of theelectroplating apparatus that were described herein. For example, as itwas described, in some embodiments, the asymmetric shield is anasymmetric HRVA, and in some embodiments components of the plating cell,such as thieves, shields, or the HRVA are configured to be rotated.

The apparatus and methods described herein may be used in conjunctionwith lithographic patterning tools or processes, for example, for thefabrication or manufacture of semiconductor devices, displays, LEDs,photovoltaic panels and the like. Typically, though not necessarily,such tools/processes will be used or conducted together in a commonfabrication facility. Lithographic patterning of a film typicallycomprises some or all of the following steps, each step enabled with anumber of possible tools: (1) application of photoresist on a workpiece,i.e., substrate, using a spin-on or spray-on tool; (2) curing ofphotoresist using a hot plate or furnace or UV curing tool; (3) exposingthe photoresist to visible or UV or x-ray light with a tool such as awafer stepper; (4) developing the resist so as to selectively removeresist and thereby pattern it using a tool such as a wet bench; (5)transferring the resist pattern into an underlying film or workpiece byusing a dry or plasma-assisted etching tool; and (6) removing the resistusing a tool such as an RF or microwave plasma resist stripper. Oneembodiment is a method as described herein further including: applyingphotoresist to the wafer after electroplating for both radial andazimuthal uniformity; exposing the photoresist to an energy source;patterning the resist and transferring the pattern to the wafer; andselectively removing the photoresist from the wafer. One embodiment issystem including an apparatus as described herein further comprising astepper. In some embodiments, used in TSV and WLP processing, thephotoresist is applied and patterned to provide a surface having one ormore recessed features prior to electroplating; the features are filledwith metal during electroplating, and the photoresist is removed afterelectroplating.

Azimuthally Asymmetric and Multi-Segmented Anodes and AzimuthallyAsymmetric and Multi-Segmented Electrodes Configured to Function Both asan Anode and a Cathode

In the preceding sections the auxiliary electrodes, such as azimuthallyasymmetric and multi-segmented electrodes were primarily exemplified bythief cathodes,—negatively biased electrodes which are configured todivert ionic (plating) current. It is herein provided that in otherembodiments—auxiliary azimuthally asymmetric and auxiliarymulti-segmented anodes,—positively biased electrodes which areconfigured to donate plating current, are used to make azimuthalcorrections, instead of thieves. Yet in other embodiments, azimuthallyasymmetric and multi-segmented electrodes configured to function both asan anode and a cathode (also referred to as anode/cathodes) are usedinstead of thieves. The anode/cathode is configured to be biasedpositively (anodically) for a portion of a time, such that it is able todonate current, and negatively (cathoidcally) for another portion oftime during electroplating, when it is configured to divert current andfunctions as a current thief. Embodiments provided herein include any ofthe embodiments described above, where instead of a thief cathode, anauxiliary anode, or an auxiliary anode/cathode is used.

In general, thief cathodes, auxiliary anodes, and auxiliaryanode/cathodes are referred herein to as auxiliary electrodes. Theseinclude azimuthally asymmetric electrodes (such as C-shaped electrodes)and multi-segmented auxiliary electrodes.

The auxiliary anode may be an inert anode or dimensionally stable anode,for example generating oxygen gas, or it can be a metallic anode,creating metal ions of the plated metal. The auxiliary cathode mayundergo metal plating thereupon during use, or may undergo anothercathodic reaction, such as hydrogen evolution. Hydrogen evolution ratherthan metal plating can be enabled if plateable metal ions are excludedfrom the electrode's surface, for example, by having the auxiliaryelectrode exposed to a metal free solution, such as a solutioncontaining only acids or non-platable salts, and having the auxiliaryelectrode to be physically separated from the main chamber so as toavoid mixing of materials containing plating metal, but such that it isstill in ionic communication with the main plating chamber (housing thewafer) via an ionically conducting media that is resistant to fluidtransport (e.g. a cationic membrane).

The use of an auxiliary anode or an anode/cathode is sometimespreferable, because metal is deposited on thief cathodes duringelectroplating in many embodiments, which may lead to formation of strayparticles, flaking of the metal, and contamination of the plating bath.In contrast, auxiliary anodes are positively biased, and deposition ofmetal on their surface is avoided. Further, in some embodiments, ananode/cathode, which spends more time being positively biased thannegatively biased, is preferred for the same reason, i.e. there is a netanodic current and therefore no net buildup of metal on the electrodeover the processing complete cycle. Such anode/cathode with a “net”anode function, would not accumulate deposits of metal on its surface,because any metal deposited on it during its cathodic phase would beredissolved during its anodic phase.

The auxiliary anodes and anode/cathodes are most preferably used inconjunction with shielding, because a shield, such as a symmetricalannular shield placed below the wafer to uniformly shield the waferperiphery, can render the surface of the wafer (e.g., at its periphery)generally deficient in plating current (a “cold” area that would resultin thinner than desired plating). The primary parameter influencing themagnitude of the symmetrical annular shields' effectiveness and range ofarea of influence causing the edge-region-deficient plating relative tomore centrally located regions of the wafer is shields' size (theshields inner-most diameter of current blocking). The asymmetry of thewafer will introduce one or more regions at one or more azimuthalpositions that are more or less deficient in current than the rest ofthe wafer. By using an appropriately selected shield size, azimuthalregions of wafer near missing die or features can be tuned to exhibitsomewhat thicker-than-average features, while simultaneously; azimuthalregions of the wafer without missing die/feature will then tend to bedeficient in current and thickness. Using a shield that blocks more ofthe edge (smaller inner diameter) might create a situation where boththe missing die regions and the general edge regions are both deficient,but the missing die region is somewhat less deficient than the generaledge. Or, a shield having an inner diameter larger than both of thepreceeding two examples might be selected, in which case both thegeneral edge and the missing die edge are thicker than the wafer center,but the missing die region features are the thickest on the wafer. Theauxiliary “C” shaped electrode can then correct for any other thesecases, i.e. both cases of excess and for deficiencies, by donating orscavenging edge plating current to a different extent and/or differentsign (anodic vs. cathodic) at different azimuthal locations. Theauxiliary anode/cathodes can correct this problem by donating current toa selected azimuthal positions of the wafer (during the time theanode/cathode is positively biased) and by diverting current from adifferent azimuthal position of the wafer (during the time theanode/cathode is negatively biased).

FIG. 10A provides an illustration for use of a C-shaped anode/cathodefor correcting azimuthal uniformity in a wafer having missing features.FIG. 10A shows four views of the wafer as it rotates wherein the shieldhas a moderate amount of edge extension, sized such that the missingdie/feature region will be slightly thick, and the rest of the waferedge will be slightly thin. The views 1001, 1003, 1005, and 1007 aretaken at different timepoints as the wafer rotates around its centralaxis. The speed of the rotation can be constant (most common for thisembodiment), but can also be varied, during the rotation. The graphbelow shows levels of anodic and cathodic currents supplied to aC-shaped auxiliary electrode over the period of the rotation and duringthese four time points and wafer angular positions. In view 1001, themissing die region 1009 is proximate to the C-shaped auxiliary electrode1011. The shield 1020 is “moderate” in size, centered between creating aslightly thick region in the missing die region and slightly thin in thegeneral edge region. Therefore, without applying corrective cathodiccurrent, this region facing the C-shaped auxiliary electrode would endup being thick. To alleviate current crowding at the missing die area,the C-shaped electrode functions as a cathode at this point in time, andis biased negatively such as to divert the current from the missing dieregion. In the views, 1003, 1005, and 1007 the wafer rotates, such thatthe missing die region 1009 is moved away from the C-shaped auxiliaryelectrode 1011. At these three timepoints, the electrode is biasedpositively (anodically) such that it can donate current to the peripheryof the wafer in its proximity. Thus, during one full rotation of thewafer, the electrode spends a portion of time biased as a cathode and aportion of time biased as an anode, and applied current levels(magnitudes) and the type (signs) of bias are correlated with therotation of the wafer in such a way as to provide a specific correctionto a selected azimuthal position of the wafer (in this case, a missingdie region). The illustration shown in FIG. 10A can be used, forexample, in conjunction with moderate shielding, where most portions ofthe wafer are “cold” (experience not sufficient current requiringdonation from an auxiliary electrode), and the missing die portion is“hot” (experiences current crowding that needs to be diverted).

In some embodiments, for example with heavy shielding of waferperiphery, the wafer periphery may be very “cold”, while the missing dierefion is less “cold”, such that all azimuthal positions require currentdonation by an auxiliary anode, but to a different extent. This isillustrated in FIG. 10B having heavy shield 1021, where the currentprovided to the C-shaped electrode is always anodic, but is provided ata lower level, when the missing die region (selected azimuthal position)is in the proximity of the electrode. The anodic current is increased,when the missing die region is rotated away from the electrode, such asto donate more current to colder regions of wafer periphery. Thus,during one full rotation of the wafer, the electrode spends a portion oftime biased as an anode at a first power level (or current level) and aportion of time biased as an anode at a higher power level (or currentlevel), where the current levels are correlated with the rotation of thewafer in such a way as to provide a specific correction to a selectedazimuthal position of the wafer.

In some embodiments, for example when the shielding is light thecathodic current level provided to the anode/cathode may besubstantially greater than an anodic current level. This is illustrated,for example, in FIG. 10C. For the same type of wafer, the light shield1022 requires that the level of cathodic current for the missing dieregion would be greater than in either of the two preceding examples,and the anodic current supplied during the general edge exposure to theC-shaped electrode is much smaller (or could even also be cathodic,depending on the particulars of the wafer, shield, and cell design).

Yet in another embodiment, e.g., with little or no general symmetricshielding, the auxiliary C-shaped electrode can function as a cathodeonly. That is, a first level of cathodic current is supplied to theelectrode when it is in the proximity of the selected azimuthalposition, and a different level of cathodic current is supplied when theselected position is rotated away from the C-shaped auxiliary cathode.Thus, during one full rotation of the wafer, the electrode spends aportion of time biased as a cathode at a first power level (or currentlevel) and a portion of time biased as a cathode at a different powerlevel (or current level), where the power levels are correlated with therotation of the wafer in such a way as to provide a specific correctionto a selected azimuthal position of the wafer.

Note that even in the absence of a missing die or feature region, theapplication of current (anodic or cathodic) can be used to tune thegeneral edge thickness distribution, and therefore, the use of theapparatus is not limited to operations with wafers having azimuthallynon-uniform patterns. Rather, this design is useful for both cases ofedge corrections, those having and those not having azimuthalnon-uniform patterns.

The embodiment illustrated in FIGS. 10A-10C relates to a method in whichthe power provided to the asymmetric auxiliary electrode is correlatedwith wafer rotation such as to provide a different level of platingcurrent to a selected azimuthal position on the wafer relative adifferent azimuthal position (having a same average arc length and asame average radial position), and to thereby divert and/or donateplating current differently to the selected azimuthal position. Theapparatus configured to perform this method of electroplating includes acontroller and an associated encoder programmed to correlate powerlevels of the auxiliary electrode and/or polarity of the auxiliaryelectrode, with the position of the selected azimuthal portion of thewafer (e.g., missing die).

In an alternative embodiment, azimuthally asymmetric electrodes (e.g.,C-shaped anodes, cathodes or anode/cathodes) or multi-segmentedelectrodes are found useful even when a constant power level is appliedto them for general correction of plating current.

The position of the electrode relative to the wafer edge, and/orconfinement of the auxiliary electrodes line of current, can be ofsignificant importance. In some embodiments, it is preferable that theauxiliary electrode (such as a C-shaped anode, cathode or anode/cathode)resides in close proximity of the wafer substrate. Preferably, thedistance between the substrate and the electrode should be no more than0.2 of the radius of a circular substrate. At this distance, theelectrode is particularly effective at correcting ionic currentenvironment at the substrate surface. At larger distances, the auxiliaryelectrode effect will be much less pronounced because ionic currentdiversion/donation will be less preferentially-favored right in front ofthe electrode face, and diffused over a larger area of the wafercomprising many azimuthal positions, potentially making the control ofthe process somewhat more difficult. However, in close proximity thediversion and/or donation of current by the electrode can be focused onthe specific azimuthal region that needs to be corrected. The auxiliaryanodes provided herein are distinct from the azimuthally asymmetricanodes located at larger distances from the wafer.

Alternatively, or in addition to proximity focusing described above, theauxiliary electrode may be housed in a confinement structure, whichprevents the donated/diverted current from being substantiallydistributed in the x-y direction. A top view of the apparatus having aC-shaped auxiliary electrode 1103 in an azimuthal current flowconfinement structure 1101 is shown in FIG. 11, where the confinementstructure confines the exposure of current from the auxiliary electrodeto a small area in the proximity of the wafer 101. An isometric view ofa similar but not identical structure is shown in FIG. 12. The auxiliaryelectrode can also be housed in a completely separate chamber, with anelectrolyte-containing channel or similar confining andangular-influence-defining region connecting it to the main platingchamber at the desired location and angular extent. Often this isreferred to as the construction of a “virtual auxiliary electrode”,where the positioning/location of the virtual electrode coincides withthe connective channel opening of the auxiliary chamber to the mainplating chamber.

It is noted that with the use of confinement or virtual chambers, theshape of the physical electrode itself becomes less important, as theshape of the diverted and/or donated current will be defined by theshape of the confinement structure housing the electrode or its opening,where the confinement structure essentially serves as a virtualauxiliary electrode.

FIG. 12 is an isometric schematic of an exemplary embodiment of aplating cell upper chamber 1200, in which a wafer and wafer holder wouldreside above and rotate in close proximity thereover (but the wafer andholder not shown). A cell's outer circular fluid containment body 1201has an upper fluid confinement weir wall 1206 around most of thecircumference. In the embodiment shown, the center of the cell is a HRVAplate or flow diffuser 1203 (the large number of small holes in theplate are not shown for simplicity). Around the edge of the HRVA andresiding under the wafer edge is a symmetrical annular shield 1202. Overa portion of the circumference of the upper chamber is a “C” shapedauxiliary electrode 1204. In a preferred embodiment, in the area beyondauxiliary electrode 1204 (slightly more removed from the center of thecell) is a region where the upper chamber's 1200 weir wall 1206 is cutout to a slightly lower level, allowing for the preferential channelingof fluid flow across and around the solid or porous (e.g. screen)auxiliary electrode, enabling the supply of adequate convection andremoval of any particles or bubbles from the cell.

Described Methods are not Limited to Electroplating

It is understood that some aspects of the invention pertaining to theazimuthal correction described herein can be applied to many other filmdeposition and removal applications beyond electrodeposition, with theappropriate application and consideration of the known-in-the artdifferences in the physical mechanism and modus-operendi of otherdeposition and removal technologies. For example, a C-shaped orhorse-shoe auxiliary target would be suitable to enable azimuthalvariable rates of deposition on a rotating substrate, or an asymmetricphysical mask placed similar to that described here, in front of arotating wafer inside a plasma etching apparatus, would lead to anangularly controllable rate of etching at the edge and at a particularangular location on the wafer edge.

System Controller:

Electroplating apparatus as described herein includes hardware foraccomplishing the process operations and a system controller havinginstructions for controlling process operations in accordance with thepresent invention. For example, a rotational digital encoder, waferholder that rotates the wafer, any moving shield elements, HRVA, powerlevels applied to the auxiliary asymmetric or multi-segmentedelectrodes, etc. are controlled and synchronized by a system controller.The system controller will typically include one or more memory devicesand one or more processors configured to execute the instructions sothat the apparatus will perform a method in accordance with the presentinvention. Machine-readable media containing instructions forcontrolling process operations in accordance with the present inventionmay be coupled to the system controller.

1. A method of electroplating a metal on a cathodically biased substratewhile controlling azimuthal uniformity, the method comprising: (a)providing the substrate into an electroplating apparatus configured forrotating the substrate during electroplating, wherein the apparatuscomprises an anode and a stationary auxiliary azimuthally asymmetriccathode; and (b) electroplating the metal on the substrate whilerotating the substrate, and while providing power to the auxiliaryazimuthally asymmetric cathode in correlation with the rotation of thesubstrate, such that the auxiliary azimuthally asymmetric cathodediverts plating current from a first portion of the substrate at aselected azimuthal position of the substrate differently than from asecond portion of the substrate having the same average arc length andthe same average radial position and residing at a different azimuthalangular position.
 2. The method of claim 1, wherein the auxiliaryazimuthally asymmetric cathode is C-shaped.
 3. The method of claim 1,wherein the auxiliary azimuthally asymmetric cathode is in an azimuthalcurrent flow confinement structure.
 4. The method of claim 1, whereinthe auxiliary azimuthally asymmetric cathode is housed in a separatechamber and the exposure of plating current to the auxiliary cathode isthrough at least one channel that diverts current into a region of thecell near the periphery of the substrate over an arc angle of less thanabout 120 degrees.